The value of 0 can represent a valid hotkey ID, so make sure that when
we initialize a hotkey variable, that we use OBS_INVALID_HOTKEY_ID or
OBS_INVALID_HOTKEY_PAIR_ID and not 0.
This fixes a bug where scene item hotkey pair IDs would be initialized
to 0, and it would unregister valid unrelated hotkeys. Particularly,
the start/stop streaming hotkey pair ID, which would commonly be the
first hotkey pair created, thus having the hotkey pair ID of 0. The
start/streaming hotkey pair would unintentionally be unregistered via
code in obs-scene.c.
caceb62328