Fix labels plugin wallet popping bug.

plugins/labels/labels.py

@@ -147,3 +147,6 @@ class LabelsPlugin(BasePlugin):
         t = threading.Thread(target=self.pull_thread, args=(wallet, False))
         t.setDaemon(True)
         t.start()
+
+    def stop_wallet(self, wallet):
+        self.wallets.pop(wallet, None)

plugins/labels/qt.py

@@ -62,5 +62,4 @@ class Plugin(LabelsPlugin):
 
     @hook
     def on_close_window(self, window):
-        self.wallets.pop(window.wallet)
-
+        self.stop_wallet(window.wallet)