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, 10 insertions, 17 deletions

diff --git a/engines/sherlock/detection.cpp b/engines/sherlock/detection.cpp
index 9184fd8e88..a0598dcb46 100644
--- a/engines/sherlock/detection.cpp
+++ b/engines/sherlock/detection.cpp
@@ -233,7 +233,10 @@ SaveStateDescriptor SherlockMetaEngine::querySaveMetaInfos(const char *target, i
 
 	if (f) {
 		Sherlock::SherlockSavegameHeader header;
-		Sherlock::SaveManager::readSavegameHeader(f, header);
+		if (!Sherlock::SaveManager::readSavegameHeader(f, header, false)) {
+			delete f;
+			return SaveStateDescriptor();
+		}
 		delete f;
 
 		// Create the return descriptor
diff --git a/engines/sherlock/saveload.cpp b/engines/sherlock/saveload.cpp
index 9d203a6a27..ca27f57a97 100644
--- a/engines/sherlock/saveload.cpp
+++ b/engines/sherlock/saveload.cpp
@@ -103,13 +103,9 @@ SaveStateList SaveManager::getSavegameList(const Common::String &target) {
 			Common::InSaveFile *in = g_system->getSavefileManager()->openForLoading(*file);
 
 			if (in) {
-				if (!readSavegameHeader(in, header))
-					continue;
+				if (readSavegameHeader(in, header))
+					saveList.push_back(SaveStateDescriptor(slot, header._saveName));
 
-				saveList.push_back(SaveStateDescriptor(slot, header._saveName));
-
-				header._thumbnail->free();
-				delete header._thumbnail;
 				delete in;
 			}
 		}
@@ -119,9 +115,8 @@ SaveStateList SaveManager::getSavegameList(const Common::String &target) {
 	return saveList;
 }
 
-bool SaveManager::readSavegameHeader(Common::InSaveFile *in, SherlockSavegameHeader &header) {
+WARN_UNUSED_RESULT bool SaveManager::readSavegameHeader(Common::InSaveFile *in, SherlockSavegameHeader &header, bool skipThumbnail) {
 	char saveIdentBuffer[SAVEGAME_STR_SIZE + 1];
-	header._thumbnail = nullptr;
 
 	// Validate the header Id
 	in->read(saveIdentBuffer, SAVEGAME_STR_SIZE + 1);
@@ -138,9 +133,9 @@ bool SaveManager::readSavegameHeader(Common::InSaveFile *in, SherlockSavegameHea
 	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;
+	}
 
 	// Read in save date/time
 	header._year = in->readSint16LE();
@@ -212,11 +207,6 @@ void SaveManager::loadGame(int slot) {
 	if (!readSavegameHeader(saveFile, header))
 		error("Invalid savegame");
 
-	if (header._thumbnail) {
-		header._thumbnail->free();
-		delete header._thumbnail;
-	}
-
 	// Synchronize the savegame data
 	Serializer s(saveFile, nullptr);
 	s.setVersion(header._version);
diff --git a/engines/sherlock/saveload.h b/engines/sherlock/saveload.h
index 59b0b26d6e..6348b0f668 100644
--- a/engines/sherlock/saveload.h
+++ b/engines/sherlock/saveload.h
@@ -105,7 +105,7 @@ public:
 	/**
 	 * Read in the header information for a savegame
 	 */
-	static bool readSavegameHeader(Common::InSaveFile *in, SherlockSavegameHeader &header);
+	WARN_UNUSED_RESULT static bool readSavegameHeader(Common::InSaveFile *in, SherlockSavegameHeader &header, bool skipThumbnail = true);
 
 	/**
 	 * Return the index of the button the mouse is over, if any