Perform full rectangle intersection for empty rects

If we don't do that, we leave the x and y values uninitialized.

Fixes libsdl-org/sdl12-compat#365

(cherry picked from commit ffd0ca4)

Author: slouken

src/video/SDL_rect_impl.h

@@ -31,8 +31,6 @@ SDL_bool SDL_HASINTERSECTION(const RECTTYPE *A, const RECTTYPE *B)
     } else if (!B) {
         SDL_InvalidParamError("B");
         return SDL_FALSE;
-    } else if (SDL_RECTEMPTY(A) || SDL_RECTEMPTY(B)) {
-        return SDL_FALSE; /* Special cases for empty rects */
     }
 
     /* Horizontal intersection */
@@ -79,10 +77,6 @@ SDL_bool SDL_INTERSECTRECT(const RECTTYPE *A, const RECTTYPE *B, RECTTYPE *resul
     } else if (!result) {
         SDL_InvalidParamError("result");
         return SDL_FALSE;
-    } else if (SDL_RECTEMPTY(A) || SDL_RECTEMPTY(B)) { /* Special cases for empty rects */
-        result->w = 0;
-        result->h = 0;
-        return SDL_FALSE;
     }
 
     /* Horizontal intersection */