Fix for dropped joystick events contributed by Simon <simon@mungewell.org>

In my system SDL2 is dropping a chunk of joystick events, which result in
a 'stuck brake/accelerator' whilst playing a racing simulator. This
basically means SDL2 is unsuitable for use at this point...

The patch below detects this situation and forces a re-read of all
attached joystick axis - thus resync to the correct/current pedal
positions.

src/joystick/linux/SDL_sysjoystick_c.h

@@ -50,4 +50,8 @@ struct joystick_hwdata
         int used;
         int coef[3];
     } abs_correct[ABS_MAX];
+
+    int fresh;
 };
+
+/* vi: set ts=4 sw=4 expandtab: */