Fix a couple of warnings

src/video/SDL_fillrect.c

@@ -274,7 +274,7 @@ static void
 SDL_FillRect2(Uint8 * pixels, int pitch, Uint32 color, int w, int h)
 {
     int n;
-    Uint8 *p = NULL;
+    Uint16 *p = NULL;
 
     while (h--) {
         n = w;

src/video/x11/SDL_x11shape.c

@@ -90,7 +90,7 @@ int
 X11_SetWindowShape(SDL_WindowShaper *shaper,SDL_Surface *shape,SDL_WindowShapeMode *shape_mode) {
     SDL_ShapeData *data = NULL;
     SDL_WindowData *windowdata = NULL;
-    Pixmap shapemask = NULL;
+    Pixmap shapemask;
 
     if(shaper == NULL || shape == NULL || shaper->driverdata == NULL)
         return -1;