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.

3 files changed, 7 insertions, 9 deletions

diff --git a/engines/bbvs/bbvs.h b/engines/bbvs/bbvs.h
index 9fb6b9cac3..a9d37c2551 100644
--- a/engines/bbvs/bbvs.h
+++ b/engines/bbvs/bbvs.h
@@ -417,7 +417,7 @@ public:
 	const char *getSavegameFilename(int num);
 	bool existsSavegame(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);
 
 	void allocSnapshot();
 	void freeSnapshot();
diff --git a/engines/bbvs/detection.cpp b/engines/bbvs/detection.cpp
index 1b2c644dda..b30c6d3f2d 100644
--- a/engines/bbvs/detection.cpp
+++ b/engines/bbvs/detection.cpp
@@ -124,7 +124,7 @@ SaveStateList BbvsMetaEngine::listSaves(const char *target) const {
 		if (slotNum >= 0 && slotNum <= 999) {
 			Common::InSaveFile *in = saveFileMan->openForLoading(file->c_str());
 			if (in) {
-				if (Bbvs::BbvsEngine::readSaveHeader(in, false, header) == Bbvs::BbvsEngine::kRSHENoError) {
+				if (Bbvs::BbvsEngine::readSaveHeader(in, header) == Bbvs::BbvsEngine::kRSHENoError) {
 					saveList.push_back(SaveStateDescriptor(slotNum, header.description));
 				}
 				delete in;
@@ -142,7 +142,7 @@ SaveStateDescriptor BbvsMetaEngine::querySaveMetaInfos(const char *target, int s
 	if (in) {
 		Bbvs::BbvsEngine::SaveHeader header;
 		Bbvs::BbvsEngine::kReadSaveHeaderError error;
-		error = Bbvs::BbvsEngine::readSaveHeader(in, true, header);
+		error = Bbvs::BbvsEngine::readSaveHeader(in, header, false);
 		delete in;
 		if (error == Bbvs::BbvsEngine::kRSHENoError) {
 			SaveStateDescriptor desc(slot, header.description);
diff --git a/engines/bbvs/saveload.cpp b/engines/bbvs/saveload.cpp
index 74c255c860..d4782aad39 100644
--- a/engines/bbvs/saveload.cpp
+++ b/engines/bbvs/saveload.cpp
@@ -27,7 +27,7 @@
 
 namespace Bbvs {
 
-BbvsEngine::kReadSaveHeaderError BbvsEngine::readSaveHeader(Common::SeekableReadStream *in, bool loadThumbnail, SaveHeader &header) {
+WARN_UNUSED_RESULT BbvsEngine::kReadSaveHeaderError BbvsEngine::readSaveHeader(Common::SeekableReadStream *in, SaveHeader &header, bool skipThumbnail) {
 
 	header.version = in->readUint32LE();
 	if (header.version > BBVS_SAVEGAME_VERSION)
@@ -38,10 +38,8 @@ BbvsEngine::kReadSaveHeaderError BbvsEngine::readSaveHeader(Common::SeekableRead
 	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
@@ -101,7 +99,7 @@ void BbvsEngine::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);