playlist: increase playlist version after loading state

After the state file has been loaded, the playlist version is still
"1", and "plchanges 1" returns the whole playlist.  Fix this by
increasing the playlist version after the state file has been loaded.

src/playlist_state.c

@@ -113,6 +113,8 @@ playlist_state_load(FILE *fp, struct playlist *playlist,
 			break;
 		}
 	}
+
+	queue_increment_version(&playlist->queue);
 }
 
 void