Improve closing of playist tabs

Fixes #90

app/musicmuster.py

@@ -222,20 +222,23 @@ class Window(QMainWindow, Ui_MainWindow):
         self.music.set_volume(volume)
 
     def close_playlist_tab(self):
+        self.close_tab(self.tabPlaylist.currentIndex())
+
+    def close_tab(self, index):
+        if hasattr(self.tabPlaylist.widget(index), 'is_playlist'):
+            if self.tabPlaylist.widget(index) == self.current_track_playlist_tab:
+                self.statusbar.showMessage("Can't close current track playlist",
+                                           5000)
+                return
+            if self.tabPlaylist.widget(index) == self.next_track_playlist_tab:
+                self.statusbar.showMessage("Can't close next track playlist", 5000)
+                return
+            # It's OK to close this playlist so remove from open playlist list
             with Session() as session:
                 playlist_db = session.query(Playlists).filter(
                     Playlists.id == self.visible_playlist_tab().id).one()
                 playlist_db.close(session)
-            index = self.tabPlaylist.currentIndex()
+        # Close regardless of tab type
-            self.tabPlaylist.removeTab(index)
-
-    def close_tab(self, index):
-        if self.tabPlaylist.widget(index) == self.current_track_playlist_tab:
-            self.statusbar.showMessage("Can't close current track playlist",
-                                       5000)
-        elif self.tabPlaylist.widget(index) == self.next_track_playlist_tab:
-            self.statusbar.showMessage("Can't close next track playlist", 5000)
-        else:
         self.tabPlaylist.removeTab(index)
 
     def create_note(self, session, text):

app/playlists.py

@@ -50,6 +50,7 @@ class PlaylistTab(QTableWidget):
 
         self.id = None
         self.name = None
+        self.is_playlist = True
         self.master_process = self.parent()
         self.setEditTriggers(QtWidgets.QAbstractItemView.NoEditTriggers)
         self.setAlternatingRowColors(True)