Remove unnecessary Sint16 casts

These casts are sprinkled all throughout the graphics code when creating
and initializing an SDL_Rect on the same line. Unfortunately, most of
these are unnecessary, and at worst are wasteful because they result in
narrowing a 4-byte integer into a 2-byte one when they don't need to
(SDL_Rects are made up of 4-byte integers).

Now, removing them reveals why they were placed there in the first place
- a warning is raised (-Wnarrowing) that implicit narrowing conversions
are prohibited in initializer lists in C++11. (Notably, if the
conversion wasn't narrowing, or implicit, or done in an initializer
list, it would be fine. This is a really specific prohibition that
doesn't apply if any of its sub-cases are true.)

We don't use C++11, but this warning can be easily vanquished by a
simple explicit cast to int (similar to the error of implicitly
converting void* to any other pointer in C++, which works just fine in
C), and we only need to do it when the warning is raised (not every
single time we make an SDL_Rect), so there we go.

desktop_version/src/GraphicsUtil.cpp

@@ -382,7 +382,7 @@ SDL_Surface* ApplyFilter( SDL_Surface* _src )
 
 void FillRect( SDL_Surface* _surface, const int _x, const int _y, const int _w, const int _h, const int r, int g, int b )
 {
-    SDL_Rect rect = {Sint16(_x),Sint16(_y),Sint16(_w),Sint16(_h)};
+    SDL_Rect rect = {_x, _y, _w, _h};
     Uint32 color = SDL_MapRGB(_surface->format, r, g, b);
     SDL_FillRect(_surface, &rect, color);
 }
@@ -400,7 +400,7 @@ void FillRect( SDL_Surface* _surface, const int color )
 
 void FillRect( SDL_Surface* _surface, const int x, const int y, const int w, const int h, int rgba )
 {
-    SDL_Rect rect = {Sint16(x)  ,Sint16(y) ,Sint16(w) ,Sint16(h) };
+    SDL_Rect rect = {x, y, w, h};
     SDL_FillRect(_surface, &rect, rgba);
 }