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, 8 insertions, 5 deletions

diff --git a/engines/macventure/detection.cpp b/engines/macventure/detection.cpp
index c179647121..5eda420cb2 100644
--- a/engines/macventure/detection.cpp
+++ b/engines/macventure/detection.cpp
@@ -54,7 +54,7 @@ static const PlainGameDescriptor macventureGames[] = {
 
 namespace MacVenture {
 
-SaveStateDescriptor loadMetaData(Common::SeekableReadStream *s, int slot);
+SaveStateDescriptor loadMetaData(Common::SeekableReadStream *s, int slot, bool skipThumbnail = true);
 
 class MacVentureMetaEngine : public AdvancedMetaEngine {
 public:
@@ -164,7 +164,7 @@ SaveStateDescriptor MacVentureMetaEngine::querySaveMetaInfos(const char *target,
 
 	Common::InSaveFile *in = saveFileMan->openForLoading(saveFileName);
 	if (in) {
-		desc = loadMetaData(in, slot);
+		desc = loadMetaData(in, slot, false);
 		delete in;
 		return desc;
 	}
diff --git a/engines/macventure/saveload.cpp b/engines/macventure/saveload.cpp
index 89a6301318..c63b6a6951 100644
--- a/engines/macventure/saveload.cpp
+++ b/engines/macventure/saveload.cpp
@@ -42,7 +42,7 @@ namespace MacVenture {
 #define MACVENTURE_SAVE_VERSION 1 //1 BYTE
 #define MACVENTURE_DESC_LENGTH 4 //4 BYTE for the metadata length
 
-SaveStateDescriptor loadMetaData(Common::SeekableReadStream *s, int slot) {
+SaveStateDescriptor loadMetaData(Common::SeekableReadStream *s, int slot, bool skipThumbnail) {
 	// Metadata is stored at the end of the file
 	// |THUMBNAIL						|
 	// |								|
@@ -65,8 +65,11 @@ SaveStateDescriptor loadMetaData(Common::SeekableReadStream *s, int slot) {
 	s->seek(-(5 + MACVENTURE_DESC_LENGTH + metaSize), SEEK_END);
 
 	// Load the thumbnail
-	Graphics::Surface *thumb = Graphics::loadThumbnail(*s);
-	desc.setThumbnail(thumb);
+	Graphics::Surface *thumbnail;
+	if (!Graphics::loadThumbnail(*s, thumbnail, skipThumbnail)) {
+		return desc;
+	}
+	desc.setThumbnail(thumbnail);
 
 	// Load the description
 	Common::String name;