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, 15 insertions, 11 deletions

diff --git a/engines/cruise/detection.cpp b/engines/cruise/detection.cpp
index 6f5d236173..3dfd414fd2 100644
--- a/engines/cruise/detection.cpp
+++ b/engines/cruise/detection.cpp
@@ -241,9 +241,8 @@ SaveStateList CruiseMetaEngine::listSaves(const char *target) const {
 			Common::InSaveFile *in = saveFileMan->openForLoading(*file);
 			if (in) {
 				Cruise::CruiseSavegameHeader header;
-				Cruise::readSavegameHeader(in, header);
-				saveList.push_back(SaveStateDescriptor(slotNum, header.saveName));
-				delete header.thumbnail;
+				if (Cruise::readSavegameHeader(in, header))
+					saveList.push_back(SaveStateDescriptor(slotNum, header.saveName));
 				delete in;
 			}
 		}
@@ -264,7 +263,11 @@ SaveStateDescriptor CruiseMetaEngine::querySaveMetaInfos(const char *target, int
 
 	if (f) {
 		Cruise::CruiseSavegameHeader header;
-		Cruise::readSavegameHeader(f, header);
+		if (!Cruise::readSavegameHeader(f, header, false)) {
+			delete f;
+			return SaveStateDescriptor();
+		}
+
 		delete f;
 
 		// Create the return descriptor
diff --git a/engines/cruise/saveload.cpp b/engines/cruise/saveload.cpp
index a62648df08..7aaeb06905 100644
--- a/engines/cruise/saveload.cpp
+++ b/engines/cruise/saveload.cpp
@@ -43,9 +43,8 @@ struct overlayRestoreTemporary {
 
 overlayRestoreTemporary ovlRestoreData[90];
 
-bool readSavegameHeader(Common::InSaveFile *in, CruiseSavegameHeader &header) {
+WARN_UNUSED_RESULT bool readSavegameHeader(Common::InSaveFile *in, CruiseSavegameHeader &header, bool skipThumbnail) {
 	char saveIdentBuffer[6];
-	header.thumbnail = NULL;
 
 	// Validate the header Id
 	in->read(saveIdentBuffer, 6);
@@ -62,9 +61,9 @@ bool readSavegameHeader(Common::InSaveFile *in, CruiseSavegameHeader &header) {
 	while ((ch = (char)in->readByte()) != '\0') header.saveName += ch;
 
 	// Get the thumbnail
-	header.thumbnail = Graphics::loadThumbnail(*in);
-	if (!header.thumbnail)
+	if (!Graphics::loadThumbnail(*in, header.thumbnail, skipThumbnail)) {
 		return false;
+	}
 
 	return true;
 }
@@ -827,8 +826,10 @@ Common::Error loadSavegameData(int saveGameIdx) {
 
 	// Skip over the savegame header
 	CruiseSavegameHeader header;
-	readSavegameHeader(f, header);
-	delete header.thumbnail;
+	if (!readSavegameHeader(f, header)) {
+		delete f;
+		return Common::kReadingFailed;
+	}
 
 	// Synchronise the remaining data of the savegame
 	Common::Serializer s(f, NULL);
diff --git a/engines/cruise/saveload.h b/engines/cruise/saveload.h
index 6fb1f4b545..c92f0e9da5 100644
--- a/engines/cruise/saveload.h
+++ b/engines/cruise/saveload.h
@@ -38,7 +38,7 @@ struct CruiseSavegameHeader {
 
 Common::Error saveSavegameData(int saveGameIdx, const Common::String &saveName);
 Common::Error loadSavegameData(int saveGameIdx);
-bool readSavegameHeader(Common::InSaveFile *in, CruiseSavegameHeader &header);
+WARN_UNUSED_RESULT bool readSavegameHeader(Common::InSaveFile *in, CruiseSavegameHeader &header, bool skipThumbnail = true);
 void initVars();
 
 } // End of namespace Cruise