Fix creating multiple timers to update song rows UI

As it sits Pithos starts a new UI loop every time play is pressed
(maybe even more often?) and never destroys old loops. They stack up
over time creating a small memory leak of sorts. This patch makes
Pithos handle the UI loop more intelligently by starting/creating it
when needed and stopping/destroying it when it's not needed (like
when Pithos is paused). Credit for the code goes to the Exaile devs
as it's pretty much a copy and paste of their code with a little
tweaking to make it work with Pithos.

Closes #166

pithos/pithos.py

@@ -245,7 +245,7 @@ def init_core(self):
         self.gstreamer_error = ''
         self.waiting_for_playlist = False
         self.start_new_playlist = False
-
+        self.ui_loop_timer_id = 0
         self.worker = GObjectWorker()
         self.art_worker = GObjectWorker()
 
@@ -508,8 +508,8 @@ def user_play(self, *ignore):
     def play(self):
         if not self.playing:
             self.playing = True
+            self.create_ui_loop()
         self.player.set_state(Gst.State.PLAYING)
-        GLib.timeout_add_seconds(1, self.update_song_row)
         self.playpause_image.set_from_icon_name('media-playback-pause-symbolic', Gtk.IconSize.SMALL_TOOLBAR)
         self.update_song_row()
         self.emit('play-state-changed', True)
@@ -520,6 +520,7 @@ def user_pause(self, *ignore):
 
     def pause(self):
         self.playing = False
+        self.destroy_ui_loop()
         self.player.set_state(Gst.State.PAUSED)
         self.playpause_image.set_from_icon_name('media-playback-start-symbolic', Gtk.IconSize.SMALL_TOOLBAR)
         self.update_song_row()
@@ -534,6 +535,7 @@ def stop(self):
             self.emit("song-ended", prev)
 
         self.playing = False
+        self.destroy_ui_loop()
         self.player.set_state(Gst.State.NULL)
         self.emit('play-state-changed', False)
 
@@ -845,6 +847,15 @@ def update_song_row(self, song = None):
             self.songs_model[song.index][2] = self.song_icon(song) or ""
         return self.playing
 
+    def create_ui_loop(self):
+        if not self.ui_loop_timer_id:
+            self.ui_loop_timer_id = GLib.timeout_add_seconds(1, self.update_song_row)
+
+    def destroy_ui_loop(self):
+        if self.ui_loop_timer_id:
+            GLib.source_remove(self.ui_loop_timer_id)
+            self.ui_loop_timer_id = 0
+
     def stations_combo_changed(self, widget):
         index = widget.get_active()
         if index>=0: