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, 5 insertions, 15 deletions

diff --git a/engines/cge/cge.h b/engines/cge/cge.h
index d3f8a93c1d..668224d2f7 100644
--- a/engines/cge/cge.h
+++ b/engines/cge/cge.h
@@ -246,7 +246,7 @@ public:
 	void mainLoop();
 	void handleFrame();
 	void saveGame(int slotNumber, const Common::String &desc);
-	static bool readSavegameHeader(Common::InSaveFile *in, SavegameHeader &header);
+	WARN_UNUSED_RESULT static bool readSavegameHeader(Common::InSaveFile *in, SavegameHeader &header, bool skipThumbnail = true);
 	void switchMusic();
 	void selectPocket(int n);
 	void expandSprite(Sprite *spr);
diff --git a/engines/cge/cge_main.cpp b/engines/cge/cge_main.cpp
index b60f201cb0..fcbbf34a4d 100644
--- a/engines/cge/cge_main.cpp
+++ b/engines/cge/cge_main.cpp
@@ -242,10 +242,6 @@ bool CGEEngine::loadGame(int slotNumber, SavegameHeader *header, bool tiny) {
 			delete readStream;
 			return true;
 		}
-
-		// Delete the thumbnail
-		saveHeader.thumbnail->free();
-		delete saveHeader.thumbnail;
 	}
 
 	// Get in the savegame
@@ -424,9 +420,7 @@ void CGEEngine::syncGame(Common::SeekableReadStream *readStream, Common::WriteSt
 	}
 }
 
-bool CGEEngine::readSavegameHeader(Common::InSaveFile *in, SavegameHeader &header) {
-	header.thumbnail = nullptr;
-
+WARN_UNUSED_RESULT bool CGEEngine::readSavegameHeader(Common::InSaveFile *in, SavegameHeader &header, bool skipThumbnail) {
 	// Get the savegame version
 	header.version = in->readByte();
 	if (header.version > kSavegameVersion)
@@ -439,9 +433,9 @@ bool CGEEngine::readSavegameHeader(Common::InSaveFile *in, SavegameHeader &heade
 		header.saveName += ch;
 
 	// Get the thumbnail
-	header.thumbnail = Graphics::loadThumbnail(*in);
-	if (!header.thumbnail)
+	if (!Graphics::loadThumbnail(*in, header.thumbnail, skipThumbnail)) {
 		return false;
+	}
 
 	// Read in save date/time
 	header.saveYear = in->readSint16LE();
diff --git a/engines/cge/detection.cpp b/engines/cge/detection.cpp
index 482591bf50..cae2e036b9 100644
--- a/engines/cge/detection.cpp
+++ b/engines/cge/detection.cpp
@@ -221,10 +221,6 @@ SaveStateList CGEMetaEngine::listSaves(const char *target) const {
 					// Valid savegame
 					if (CGE::CGEEngine::readSavegameHeader(file, header)) {
 						saveList.push_back(SaveStateDescriptor(slotNum, header.saveName));
-						if (header.thumbnail) {
-							header.thumbnail->free();
-							delete header.thumbnail;
-						}
 					}
 				} else {
 					// Must be an original format savegame
@@ -253,7 +249,7 @@ SaveStateDescriptor CGEMetaEngine::querySaveMetaInfos(const char *target, int sl
 		f->read(buffer, kSavegameStrSize + 1);
 
 		bool hasHeader = !strncmp(buffer, CGE::savegameStr, kSavegameStrSize + 1) &&
-			CGE::CGEEngine::readSavegameHeader(f, header);
+			CGE::CGEEngine::readSavegameHeader(f, header, false);
 		delete f;
 
 		if (!hasHeader) {