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, 12 insertions, 4 deletions

diff --git a/engines/lab/lab.h b/engines/lab/lab.h
index 2a1e527098..aedf0181ec 100644
--- a/engines/lab/lab.h
+++ b/engines/lab/lab.h
@@ -502,7 +502,7 @@ private:
 	void handleTrialWarning();
 };
 
-bool readSaveGameHeader(Common::InSaveFile *in, SaveGameHeader &header);
+WARN_UNUSED_RESULT bool readSaveGameHeader(Common::InSaveFile *in, SaveGameHeader &header, bool skipThumbnail = true);
 
 } // End of namespace Lab
 
diff --git a/engines/lab/savegame.cpp b/engines/lab/savegame.cpp
index 656595e3e5..46ef1486f0 100644
--- a/engines/lab/savegame.cpp
+++ b/engines/lab/savegame.cpp
@@ -76,7 +76,7 @@ void LabEngine::writeSaveGameHeader(Common::OutSaveFile *out, const Common::Stri
 	out->writeUint32BE(playTime);
 }
 
-bool readSaveGameHeader(Common::InSaveFile *in, SaveGameHeader &header) {
+WARN_UNUSED_RESULT bool readSaveGameHeader(Common::InSaveFile *in, SaveGameHeader &header, bool skipThumbnail) {
 	uint32 id = in->readUint32BE();
 
 	// Check if it's a valid ScummVM savegame
@@ -98,7 +98,11 @@ bool readSaveGameHeader(Common::InSaveFile *in, SaveGameHeader &header) {
 	header._descr.setDescription(saveName);
 
 	// Get the thumbnail
-	header._descr.setThumbnail(Graphics::loadThumbnail(*in));
+	Graphics::Surface *thumbnail;
+	if (!Graphics::loadThumbnail(*in, thumbnail, skipThumbnail)) {
+		return false;
+	}
+	header._descr.setThumbnail(thumbnail);
 
 	uint32 saveDate = in->readUint32BE();
 	uint16 saveTime = in->readUint16BE();
@@ -174,7 +178,11 @@ bool LabEngine::loadGame(int slot) {
 		return false;
 
 	SaveGameHeader header;
-	readSaveGameHeader(file, header);
+	if (!readSaveGameHeader(file, header)) {
+		delete file;
+		return false;
+	}
+
 	_roomNum = file->readUint16LE();
 	_music->checkRoomMusic(1, _roomNum);
 	_direction = file->readUint16LE();