Fix for high CPU usage on Windows

Hi,
I have a patch for high CPU usage caused by the joystick detect
thread. This issue consumes a non-trivial amount of power and heck, Steam
is popular enough to the point where I think this might even have a
measurable impact on carbon emissions. Patch can be found at
https://bitbucket.org/sherief/sdl2/commits/6c8c2a10cac60ebbd026523d374b246d1fadde65

- Sherief