[fridrich]

When playback is stopped from mpv itself (the on-screen controller's stop, a keyboard shortcut, or the stream ending), Hypnotix doesn't notice. The player area stays black, the channel name and URL remain, and active_channel is still set.

Hypnotix only observes core-idle, which it uses for the screensaver inhibit. core-idle is also true while paused, so it can't tell a stop from a pause.

This change:

• observes mpv's idle-active property, which is only true when no file is loaded, and calls on_stop_button() when it becomes true
• sets an is_changing_channel flag around play_async(), because mpv is briefly idle between stop() and loading the next channel, and that must not count as a stop
• re-reads idle_active in the handler, because the handler runs later on the GTK main loop and a new channel may have started by then
• makes on_stop_button() clear the channel name/URL and show the empty page, instead of leaving the black player area

Tested: stopping from the OSD while playing and while paused returns to the empty page.

[fridrich]

@mtwebster this could be interesting?