This is a multi-part fix, and is the 2nd attempt at a fix for Bug 5034. Here
are the problems being addressed:
1. On macOS 10.14.x and earlier, trying to call IOHIDDeviceUnscheduleFromRunLoop
without a prior, paired call to IOHIDDeviceScheduleWithRunLoop, appears to
lead to a crash. A per-device flag has been added to make sure that these
calls are paired.
2. DARWIN_JoystickDetect was free'ing its SDL_joystick's hwdata field
(via FreeDevice) without setting it to NULL, and DARWIN_JoystickRumble wasn't
checking for a NULL hwdata. FreeDevice will now set hwdata to NULL and
DARWIN_JoystickRumble will check for a NULL hwdata.
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