[SirFancyBacon]

Build the port without warnings

The PC build gave nine compiler warnings. This clears them all without changing what the game does.
fixes #242

• battlemenu.cpp: the debug weapon-stat cheat printed "now 20%\n", an invalid conversion.
  It prints the percent sign now (%%).
• menu_dungeon.cpp: ConvDebugSelectToExcelListNo rejected the numbers above the Scorpion
  (352) and below Super Steve (312). That range is empty, and retail's source has the same check, so
  it never rejected anything. The dead check is gone.
• Two variables read before being set, in dungeonmap.cpp and menu_save.cpp. Retail reads
  them the same way. The build's zero-initialization already made them zero; they now start at zero
  explicitly.
  • event_x and event_y are the Atla events' origin.
  • slot is the event item board's pick past its last item.
• dun/gameloop.cpp, editground.cpp: six memcpy calls copy an effect or a map part over
  another object of the same class, so the vtable pointer they copy is the class's own. Both ends
  are cast to void * to tell the compiler this is deliberate.

Testing

• The Linux build has no warnings.
• The test suite passes, apart from the GPU tests that need the Vulkan validation layer or a
  hardware renderer.