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/prince/detection.cpp b/engines/prince/detection.cpp
index ce80fe5cab..ef3128ae09 100644
--- a/engines/prince/detection.cpp
+++ b/engines/prince/detection.cpp
@@ -208,10 +208,6 @@ SaveStateList PrinceMetaEngine::listSaves(const char *target) const {
 					// Valid savegame
 					if (Prince::PrinceEngine::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
@@ -239,7 +235,7 @@ SaveStateDescriptor PrinceMetaEngine::querySaveMetaInfos(const char *target, int
 		f->read(buffer, kSavegameStrSize + 1);
 
 		bool hasHeader = !strncmp(buffer, kSavegameStr, kSavegameStrSize + 1) &&
-			Prince::PrinceEngine::readSavegameHeader(f, header);
+			Prince::PrinceEngine::readSavegameHeader(f, header, false);
 		delete f;
 
 		if (!hasHeader) {
diff --git a/engines/prince/prince.h b/engines/prince/prince.h
index 32e37e0774..c264125895 100644
--- a/engines/prince/prince.h
+++ b/engines/prince/prince.h
@@ -290,7 +290,7 @@ public:
 
 	void playVideo(Common::String videoFilename);
 
-	static bool readSavegameHeader(Common::InSaveFile *in, SavegameHeader &header);
+	WARN_UNUSED_RESULT static bool readSavegameHeader(Common::InSaveFile *in, SavegameHeader &header, bool skipThumbnail = true);
 	Common::String generateSaveName(int slot);
 	void writeSavegameHeader(Common::OutSaveFile *out, SavegameHeader &header);
 	void syncGame(Common::SeekableReadStream *readStream, Common::WriteStream *writeStream);
diff --git a/engines/prince/saveload.cpp b/engines/prince/saveload.cpp
index 14f6078910..8832a6d1d2 100644
--- a/engines/prince/saveload.cpp
+++ b/engines/prince/saveload.cpp
@@ -44,9 +44,7 @@ namespace Prince {
 class InterpreterFlags;
 class Interpreter;
 
-bool PrinceEngine::readSavegameHeader(Common::InSaveFile *in, SavegameHeader &header) {
-	header.thumbnail = nullptr;
-
+WARN_UNUSED_RESULT bool PrinceEngine::readSavegameHeader(Common::InSaveFile *in, SavegameHeader &header, bool skipThumbnail) {
 	// Get the savegame version
 	header.version = in->readByte();
 	if (header.version > kSavegameVersion)
@@ -59,9 +57,9 @@ bool PrinceEngine::readSavegameHeader(Common::InSaveFile *in, SavegameHeader &he
 		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();
@@ -416,10 +414,6 @@ bool PrinceEngine::loadGame(int slotNumber) {
 			delete readStream;
 			return false;
 		}
-
-		// Delete the thumbnail
-		saveHeader.thumbnail->free();
-		delete saveHeader.thumbnail;
 	}
 
 	// Get in the savegame