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.

2 files changed, 4 insertions, 4 deletions

diff --git a/engines/zvision/file/save_manager.cpp b/engines/zvision/file/save_manager.cpp
index 4259937a3b..b33d33cdf1 100644
--- a/engines/zvision/file/save_manager.cpp
+++ b/engines/zvision/file/save_manager.cpp
@@ -189,7 +189,7 @@ Common::Error SaveManager::loadGame(int slot) {
 	return Common::kNoError;
 }
 
-bool SaveManager::readSaveGameHeader(Common::InSaveFile *in, SaveGameHeader &header) {
+bool SaveManager::readSaveGameHeader(Common::InSaveFile *in, SaveGameHeader &header, bool skipThumbnail) {
 	uint32 tag = in->readUint32BE();
 	// Check if it's original savegame than fill header structure
 	if (tag == MKTAG('Z', 'N', 'S', 'G')) {
@@ -232,9 +232,9 @@ bool SaveManager::readSaveGameHeader(Common::InSaveFile *in, SaveGameHeader &hea
 		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/zvision/file/save_manager.h b/engines/zvision/file/save_manager.h
index 9e816373ea..94885b650b 100644
--- a/engines/zvision/file/save_manager.h
+++ b/engines/zvision/file/save_manager.h
@@ -94,7 +94,7 @@ public:
 	Common::Error loadGame(int slot);
 
 	Common::SeekableReadStream *getSlotFile(uint slot);
-	bool readSaveGameHeader(Common::SeekableReadStream *in, SaveGameHeader &header);
+	bool readSaveGameHeader(Common::SeekableReadStream *in, SaveGameHeader &header, bool skipThumbnail = true);
 
 	void prepareSaveBuffer();
 	void flushSaveBuffer();