dataengines/mpris2: Delete Multiplexer when there is no player
When all players are closed, media player applet on the desktop still shows a track from the last player, and player control buttons are still clickable but have no effect.
Add a new signal named playerListEmptied(). When the proxy list is empty,
the signal is emitted and m_multiplexer is scheduled to be deleted, so
the media player applet on the desktop can indicate the right status of
no player opened.
Dependency
!1219 (merged) must be merged first.
Effect
| After plasmashell starts | Open Audacious | Close Audacious | |
|---|---|---|---|
| After this MR |  |
 |
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| Before this MR |  |
 |
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