SDL_x11shape.c: fix build if SDL_VIDEO_DRIVER_X11_XSHAPE isn't defined

Fixes :  https://github.com/libsdl-org/SDL/issues/10128.

src/video/x11/SDL_x11shape.c

@@ -55,9 +55,10 @@ static Uint8 *GenerateShapeMask(SDL_Surface *shape)
 
 int X11_UpdateWindowShape(SDL_VideoDevice *_this, SDL_Window *window, SDL_Surface *shape)
 {
+    int result = -1;
+
 #ifdef SDL_VIDEO_DRIVER_X11_XSHAPE
     SDL_WindowData *windowdata = window->driverdata;
-    int result = -1;
 
     /* Generate a set of spans for the region */
     if (shape) {