TITANIC: Memory leaks in save game code

[csnover]

valgrind reports from dafioram

==16727== 38,400 bytes in 1 blocks are definitely lost in loss record 2,627 of 2,668
==16727==    at 0x4C2FB45: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==16727==    by 0x49ABB8: Graphics::Surface::create(unsigned short, unsigned short, Graphics::PixelFormat const&) (surface.cpp:74)
==16727==    by 0x4A1B93: Graphics::loadThumbnail(Common::SeekableReadStream&) (thumbnail.cpp:175)
==16727==    by 0x220A97: Titanic::CProjectItem::readSavegameHeader(Titanic::SimpleFile*, Titanic::TitanicSavegameHeader&) (project_item.cpp:525)
==16727==    by 0x21F6CF: Titanic::CProjectItem::loadGame(int) (project_item.cpp:192)
==16727==    by 0x347AAC: Titanic::CMainGameWindow::applicationStarting() (main_game_window.cpp:89)
==16727==    by 0x211585: Titanic::TitanicEngine::initialize() (titanic.cpp:125)
==16727==    by 0x211709: Titanic::TitanicEngine::run() (titanic.cpp:152)
==16727==    by 0x1FC228: runGame(PluginSubclass<MetaEngine> const*, OSystem&, Common::String const&) (main.cpp:263)
==16727==    by 0x1FD447: scummvm_main (main.cpp:529)
==16727==    by 0x1FA325: main (posix-main.cpp:45)
==16727== 

Build: 1.10.0git-4914-g294503f516