Fixed stack overflow in X11_CreateWindow() (thanks, rapha and Brad!).

This should be a "long" which on a 64-bit system is likely to be > 32-bits,
 causing XGetICValues() to write past the end of the variable (and stack).

Fixes Bugzilla #2513.

src/video/x11/SDL_x11window.c

@@ -361,7 +361,7 @@ X11_CreateWindow(_THIS, SDL_Window * window)
     Atom _NET_WM_WINDOW_TYPE_NORMAL;
     Atom _NET_WM_PID;
     Atom XdndAware, xdnd_version = 5;
-    Uint32 fevent = 0;
+    long fevent = 0;
 
 #if SDL_VIDEO_OPENGL_GLX || SDL_VIDEO_OPENGL_EGL
     if ((window->flags & SDL_WINDOW_OPENGL) &&