Let full_sync finish gracefully on Kodi exit

resources/lib/library_sync/get_metadata.py

@@ -118,4 +118,5 @@ class GetMetadataTask(backgroundthread.Task, common.libsync_mixin):
                           self.plex_id)
             else:
                 item['children'] = children_xml
-        self.queue.put(item)
+        if not self.isCanceled():
+            self.queue.put(item)

resources/lib/library_sync/process_metadata.py

@@ -106,4 +106,8 @@ class ProcessMetadata(backgroundthread.KillableThread, common.libsync_mixin):
         finally:
             if self.dialog:
                 self.dialog.close()
+            while not self.queue.empty():
+                # We need to empty the queue to let full_sync finish join()
+                self.queue.get()
+                self.queue.task_done()
             LOG.debug('Processing thread terminated')