ALL: Load savegame thumbnail only when necessary

This commit introduces the following changes:

1. Graphics::loadThumbnail()

   Now returns a boolean and takes a new argument skipThumbnail which
   defaults to false. In case of true, loadThumbnail() reads past the
   thumbnail data in the input stream instead of actually loading the
   thumbnail. This simplifies savegame handling where, up until now,
   many engines always read the whole savegame metadata (including
   the thumbnail) and then threw away the thumbnail when not needed
   (which is in almost all cases, the most common exception being
   MetaEngine::querySaveMetaInfos() which is responsible for loading
   savegame metadata for displaying it in the GUI launcher.

2. readSavegameHeader()

   Engines which already implement such a method (name varies) now take
   a new argument skipThumbnail (default: true) which is passed
   through to loadThumbnail(). This means that the default case for
   readSavegameHeader() is now _not_ loading the thumbnail from a
   savegame and just reading past it. In those cases, e.g.
   querySaveMetaInfos(), where we actually are interested in loading
   the thumbnail readSavegameHeader() needs to explicitely be called
   with skipThumbnail == false.

   Engines whose readSavegameHeader() (name varies) already takes an
   argument loadThumbnail have been adapted to have a similar
   prototype and semantics.
   I.e. readSaveHeader(in, loadThumbnail, header) now is
   readSaveHeader(in, header, skipThumbnail).

3. Error handling

   Engines which previously did not check the return value of
   readSavegameHeader() (name varies) now do so ensuring that possibly
   broken savegames (be it a broken thumbnail or something else) don't
   make it into the GUI launcher list in the first place.

4 files changed, 8 insertions, 10 deletions

diff --git a/engines/toltecs/detection.cpp b/engines/toltecs/detection.cpp
index 9303760057..0cd9596c8c 100644
--- a/engines/toltecs/detection.cpp
+++ b/engines/toltecs/detection.cpp
@@ -276,7 +276,7 @@ SaveStateList ToltecsMetaEngine::listSaves(const char *target) const {
 		if (slotNum >= 0 && slotNum <= 999) {
 			Common::InSaveFile *in = saveFileMan->openForLoading(file->c_str());
 			if (in) {
-				if (Toltecs::ToltecsEngine::readSaveHeader(in, false, header) == Toltecs::ToltecsEngine::kRSHENoError) {
+				if (Toltecs::ToltecsEngine::readSaveHeader(in, header) == Toltecs::ToltecsEngine::kRSHENoError) {
 					saveList.push_back(SaveStateDescriptor(slotNum, header.description));
 				}
 				delete in;
@@ -325,7 +325,7 @@ SaveStateDescriptor ToltecsMetaEngine::querySaveMetaInfos(const char *target, in
 		Toltecs::ToltecsEngine::SaveHeader header;
 		Toltecs::ToltecsEngine::kReadSaveHeaderError error;
 
-		error = Toltecs::ToltecsEngine::readSaveHeader(in, true, header);
+		error = Toltecs::ToltecsEngine::readSaveHeader(in, header, false);
 		delete in;
 
 		if (error == Toltecs::ToltecsEngine::kRSHENoError) {
diff --git a/engines/toltecs/menu.cpp b/engines/toltecs/menu.cpp
index 5fc0599c2a..c4373265e6 100644
--- a/engines/toltecs/menu.cpp
+++ b/engines/toltecs/menu.cpp
@@ -525,7 +525,7 @@ int MenuSystem::loadSavegamesList() {
 		if (slotNum >= 0 && slotNum <= 999) {
 			Common::InSaveFile *in = saveFileMan->openForLoading(file->c_str());
 			if (in) {
-				if (Toltecs::ToltecsEngine::readSaveHeader(in, false, header) == Toltecs::ToltecsEngine::kRSHENoError) {
+				if (Toltecs::ToltecsEngine::readSaveHeader(in, header) == Toltecs::ToltecsEngine::kRSHENoError) {
 					_savegames.push_back(SavegameItem(slotNum, header.description));
 					//debug("%s -> %s", file->c_str(), header.description.c_str());
 				}
diff --git a/engines/toltecs/saveload.cpp b/engines/toltecs/saveload.cpp
index 409fc97076..1f2198fc35 100644
--- a/engines/toltecs/saveload.cpp
+++ b/engines/toltecs/saveload.cpp
@@ -41,7 +41,7 @@ namespace Toltecs {
 
 #define TOLTECS_SAVEGAME_VERSION 4
 
-ToltecsEngine::kReadSaveHeaderError ToltecsEngine::readSaveHeader(Common::SeekableReadStream *in, bool loadThumbnail, SaveHeader &header) {
+WARN_UNUSED_RESULT ToltecsEngine::kReadSaveHeaderError ToltecsEngine::readSaveHeader(Common::SeekableReadStream *in, SaveHeader &header, bool skipThumbnail) {
 
 	header.version = in->readUint32LE();
 	if (header.version > TOLTECS_SAVEGAME_VERSION)
@@ -52,10 +52,8 @@ ToltecsEngine::kReadSaveHeaderError ToltecsEngine::readSaveHeader(Common::Seekab
 	while (descriptionLen--)
 		header.description += (char)in->readByte();
 
-	if (loadThumbnail) {
-		header.thumbnail = Graphics::loadThumbnail(*in);
-	} else {
-		Graphics::skipThumbnail(*in);
+	if (!Graphics::loadThumbnail(*in, header.thumbnail, skipThumbnail)) {
+		return kRSHEIoError;
 	}
 
 	// Not used yet, reserved for future usage
@@ -147,7 +145,7 @@ void ToltecsEngine::loadgame(const char *filename) {
 
 	SaveHeader header;
 
-	kReadSaveHeaderError errorCode = readSaveHeader(in, false, header);
+	kReadSaveHeaderError errorCode = readSaveHeader(in, header);
 
 	if (errorCode != kRSHENoError) {
 		warning("Error loading savegame '%s'", filename);
diff --git a/engines/toltecs/toltecs.h b/engines/toltecs/toltecs.h
index ece82f4a1a..1c9e9366c7 100644
--- a/engines/toltecs/toltecs.h
+++ b/engines/toltecs/toltecs.h
@@ -225,7 +225,7 @@ public:
 	const char *getSavegameFilename(int num);
 	static Common::String getSavegameFilename(const Common::String &target, int num);
 
-	static kReadSaveHeaderError readSaveHeader(Common::SeekableReadStream *in, bool loadThumbnail, SaveHeader &header);
+	WARN_UNUSED_RESULT static kReadSaveHeaderError readSaveHeader(Common::SeekableReadStream *in, SaveHeader &header, bool skipThumbnail = true);
 
 };