Update SDL_windowswindow.c (#6225)

Clip rectangle set to int(left+width/2) , int(top+height/2) , int(left+width/2)+1 , int(top+height/2)+1
a 1x1 box
On even-valued resolution, cursor is stable at bottom-right central pixel
On odd-valued resolution, cursor is stable at exact central pixel.
this is the desired behaviour

src/video/windows/SDL_windowswindow.c

@@ -1309,9 +1309,9 @@ WIN_UpdateClipCursor(SDL_Window *window)
                 cy = (rect.top + rect.bottom) / 2;
 
                 /* Make an absurdly small clip rect */
-                rect.left = cx - 1;
+                rect.left = cx;
                 rect.right = cx + 1;
-                rect.top = cy - 1;
+                rect.top = cy;
                 rect.bottom = cy + 1;
 
                 if (SDL_memcmp(&rect, &clipped_rect, sizeof(rect)) != 0) {