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, 8 insertions, 10 deletions

diff --git a/engines/tucker/detection.cpp b/engines/tucker/detection.cpp
index 7d07edabd3..119d60f23a 100644
--- a/engines/tucker/detection.cpp
+++ b/engines/tucker/detection.cpp
@@ -175,7 +175,7 @@ public:
 			if (ext && (slot = atoi(ext + 1)) >= 0 && slot <= Tucker::kLastSaveSlot) {
 				Common::InSaveFile *in = g_system->getSavefileManager()->openForLoading(*file);
 				if (in) {
-					if (Tucker::TuckerEngine::readSavegameHeader(in, header, false) == Tucker::TuckerEngine::kSavegameNoError) {
+					if (Tucker::TuckerEngine::readSavegameHeader(in, header) == Tucker::TuckerEngine::kSavegameNoError) {
 						saveList.push_back(SaveStateDescriptor(slot, header.description));
 					}
 
@@ -207,7 +207,7 @@ public:
 		}
 
 		Tucker::TuckerEngine::SavegameHeader header;
-		Tucker::TuckerEngine::SavegameError savegameError = Tucker::TuckerEngine::readSavegameHeader(file, header, true);
+		Tucker::TuckerEngine::SavegameError savegameError = Tucker::TuckerEngine::readSavegameHeader(file, header, false);
 		if (savegameError) {
 			delete file;
 			return SaveStateDescriptor();
diff --git a/engines/tucker/saveload.cpp b/engines/tucker/saveload.cpp
index a56ced915e..484c47e5da 100644
--- a/engines/tucker/saveload.cpp
+++ b/engines/tucker/saveload.cpp
@@ -141,7 +141,7 @@ Common::Error TuckerEngine::loadGameState(int slot) {
 }
 
 
-TuckerEngine::SavegameError TuckerEngine::readSavegameHeader(const char *target, int slot, SavegameHeader &header) {
+WARN_UNUSED_RESULT TuckerEngine::SavegameError TuckerEngine::readSavegameHeader(const char *target, int slot, SavegameHeader &header) {
 	Common::String fileName = generateGameStateFileName(target, slot);
 	Common::InSaveFile *file = g_system->getSavefileManager()->openForLoading(fileName);
 
@@ -155,7 +155,7 @@ TuckerEngine::SavegameError TuckerEngine::readSavegameHeader(const char *target,
 	return savegameError;
 }
 
-TuckerEngine::SavegameError TuckerEngine::readSavegameHeader(Common::InSaveFile *file, SavegameHeader &header, bool loadThumbnail) {
+WARN_UNUSED_RESULT TuckerEngine::SavegameError TuckerEngine::readSavegameHeader(Common::InSaveFile *file, SavegameHeader &header, bool skipThumbnail) {
 	header.version   = -1;
 	header.flags     = 0;
 	header.description.clear();
@@ -196,10 +196,8 @@ TuckerEngine::SavegameError TuckerEngine::readSavegameHeader(Common::InSaveFile
 		header.saveTime = file->readUint32LE();
 		header.playTime = file->readUint32LE();
 
-		if (loadThumbnail) {
-			header.thumbnail = Graphics::loadThumbnail(*file);
-		} else {
-			Graphics::skipThumbnail(*file);
+		if (!Graphics::loadThumbnail(*file, header.thumbnail, skipThumbnail)) {
+			return kSavegameIoError;
 		}
 	}
 
diff --git a/engines/tucker/tucker.h b/engines/tucker/tucker.h
index 4cb427fe35..e3748680fe 100644
--- a/engines/tucker/tucker.h
+++ b/engines/tucker/tucker.h
@@ -452,8 +452,8 @@ public:
 	virtual bool hasFeature(EngineFeature f) const;
 	GUI::Debugger *getDebugger() { return _console; }
 
-	static SavegameError readSavegameHeader(Common::InSaveFile *file, SavegameHeader &header, bool loadThumbnail = false);
-	static SavegameError readSavegameHeader(const char *target, int slot, SavegameHeader &header);
+	WARN_UNUSED_RESULT static SavegameError readSavegameHeader(Common::InSaveFile *file, SavegameHeader &header, bool skipThumbnail = true);
+	WARN_UNUSED_RESULT static SavegameError readSavegameHeader(const char *target, int slot, SavegameHeader &header);
 	bool isAutosaveAllowed();
 	static bool isAutosaveAllowed(const char *target);
 protected: