Fix memory leaks around gtk_get_current_event()

Merged Brian Tarricone requested to merge kelnos/xfce4-panel:current-event-memleaks into master

gtk_get_current_event() makes a copy of the event and returns the copy, which needs to be freed.

For the cases where we create a dummy event, we need to ref the GdkWindow we set on it, as gdk_event_free() will unref it.

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