Fixed return value of SDL_SaveBMP_RW() depending on set errors after NULL input. If SDL_SaveBMP_RW() was called with NULL passed as SDL_RWops argument, different values were returned depending on SDL_GetError(). If no error was set before the call (or SDL_ClearError() was called) then 0 was returned. This is wrong because nothing was saved. If an error was set before the call then -1 was returned. This was fixed by directly returning -1 for NULL input instead of deciding based on SDL_GetError(). No new error is set because this would otherwise override a maybe more useful error set in SDL_RWFromFile() which is used by SDL_SaveBMP().

--- a/src/video/SDL_bmp.c	Thu Apr 16 22:02:03 2015 +0200
+++ b/src/video/SDL_bmp.c	Thu Apr 16 22:04:35 2015 +0200
@@ -531,6 +531,10 @@
                              format.BitsPerPixel);
             }
         }
+    } else {
+        /* Set no error here because it may overwrite a more useful message from
+           SDL_RWFromFile() if SDL_SaveBMP_RW() is called from SDL_SaveBMP(). */
+        return -1;
     }
 
     if (surface && (SDL_LockSurface(surface) == 0)) {