UI: Make sure quick transition hotkey is not zeroed

Fixes a bug where removing quick transitions with no hotkey would
unintentionally remove the "start streaming" hotkey.  Hotkeys must be
initialized to OBS_INVALID_HOTKEY_ID (-1) instead of 0.  Hotkeys should
really be one-based rather than zero-based.

UI/window-basic-main.hpp

@@ -78,7 +78,7 @@ struct SavedProjectorInfo {
 struct QuickTransition {
 	QPushButton *button = nullptr;
 	OBSSource source;
-	obs_hotkey_id hotkey = 0;
+	obs_hotkey_id hotkey = OBS_INVALID_HOTKEY_ID;
 	int duration = 0;
 	int id = 0;