fix observed terminal error on initial startup 

... and when playing songs without the menu toggle option having first been activated:

<pre>

dad@dad-VirtualBox:~/.local/share/rhythmbox/plugins/lastfm_queue$ rhythmbox
Traceback (most recent call last):
  File "/home/dad/.local/share/rhythmbox/plugins/lastfm_queue/lastfm_queue.py", line 119, in playing_entry_changed
    if self.active:
AttributeError: 'LastFmQueuePlugin' object has no attribute 'active'

</pre>

I've only tested this one-line change on rb2.97 though.

At the same time I've pulled in the lated rb3compat from coverart-browser which are just python3 issues.