Hopefully fixed crash when there are no input devices

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%403424

src/video/x11/SDL_x11mouse.c

@@ -61,6 +61,7 @@ X11_InitMouse(_THIS)
     }
 
     /* we're getting the list of input devices */
+    n = 0;
     DevList = XListInputDevices(display, &n);
 
     /* we're aquiring valuators: mice, tablets, etc. */