Use that instead of using `GetOutputSurface()` directly.
For the rg99 port, we'll want to render this to the `pal_surface`
instead of output surface directly.
Might also be useful for 3ds, perhaps to render to the bottom screen.
SBmpLoadImage tried to get the size of the rest of the file incorrectly
by subtracting the current file position from the total size.
This was incorrect because file positions do not always begin at 0.
The only semi-portable way to get a size from file positions is to
subtract two file positions.
Single-player difficulty selection was implemented in a very hacky way.
Documents what's going on there and fixes a memory leak.
Memory leaks that this fixes looked like this:
```
Direct leak of 64 byte(s) in 1 object(s) allocated from:
#0 0x7f435b789f17 in operator new(unsigned long) (/lib/x86_64-linux-gnu/libasan.so.6+0xb1f17)
#1 0x5567766c62b8 in dvl::selgame_GameSelection_Select(int) ../SourceX/DiabloUI/selgame.cpp:163
#2 0x5567766d8ee8 in dvl::selhero_Load_Select(int) ../SourceX/DiabloUI/selhero.cpp:464
#3 0x5567766d6ed1 in dvl::selhero_List_Select(int) ../SourceX/DiabloUI/selhero.cpp:325
#4 0x556776692683 in dvl::UiFocusNavigationSelect() ../SourceX/DiabloUI/diabloui.cpp:396
#5 0x55677669158e in HandleMenuAction ../SourceX/DiabloUI/diabloui.cpp:223
#6 0x5567766917b9 in dvl::UiFocusNavigation(SDL_Event*) ../SourceX/DiabloUI/diabloui.cpp:277
#7 0x556776695dff in dvl::UiPollAndRender() ../SourceX/DiabloUI/diabloui.cpp:626
#8 0x5567766d94ef in UiSelHeroDialog ../SourceX/DiabloUI/selhero.cpp:512
#9 0x5567766d997f in dvl::UiSelHeroSingDialog(int (*)(int (*)(dvl::_uiheroinfo*)), int (*)(dvl::_uiheroinfo*), int (*)(dvl::_uiheroinfo*), void (*)(unsigned int, dvl::_uidefaultstats*), int*, char (*) [16], int*) ../SourceX/DiabloUI/selhero.cpp:547
#10 0x556776a44f45 in mainmenu_select_hero_dialog ../Source/mainmenu.cpp:98
#11 0x5567765f9f15 in SNetInitializeProvider ../SourceX/storm/storm_net.cpp:102
#12 0x556776c996b9 in multi_init_single ../Source/multi.cpp:826
#13 0x556776c98b1e in NetInit ../Source/multi.cpp:770
#14 0x5567767d0c0b in StartGame ../Source/diablo.cpp:375
#15 0x556776a4493d in mainmenu_init_menu ../Source/mainmenu.cpp:45
#16 0x556776a44c05 in mainmenu_single_player ../Source/mainmenu.cpp:61
#17 0x556776a454a9 in mainmenu_loop ../Source/mainmenu.cpp:152
#18 0x5567767d2892 in DiabloMain ../Source/diablo.cpp:602
#19 0x5567766e3c69 in main ../SourceX/main.cpp:34
#20 0x7f435a69ecb1 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x28cb1)
```
Epifanov Ivan
Gleb Mazovetskiy
Anders Jenbo
staphen
danie1kr
Juliano Leal Goncalves
Bardur Arantsson
Yuri Pourre
Trihedraf
Yuri Pourre