blacklist rendering edit fix

Editing of blacklist labels affected the rerendering, because it emits
the changed signal too, and it caused an exception because the address
field was missing at that time. This works around both.

src/bitmessageqt/__init__.py

@@ -3976,12 +3976,13 @@ class MyForm(settingsmixin.SMainWindow):
     def tableWidgetBlacklistItemChanged(self, item):
         if item.column() == 0:
             addressitem = self.ui.tableWidgetBlacklist.item(item.row(), 1)
-            if self.ui.radioButtonBlacklist.isChecked():
-                sqlExecute('''UPDATE blacklist SET label=? WHERE address=?''',
-                           str(item.text()), str(addressitem.text()))
-            else:
-                sqlExecute('''UPDATE whitelist SET label=? WHERE address=?''',
-                           str(item.text()), str(addressitem.text()))
+            if isinstance(addressitem, QTableWidgetItem):
+                if self.ui.radioButtonBlacklist.isChecked():
+                    sqlExecute('''UPDATE blacklist SET label=? WHERE address=?''',
+                            str(item.text()), str(addressitem.text()))
+                else:
+                    sqlExecute('''UPDATE whitelist SET label=? WHERE address=?''',
+                            str(item.text()), str(addressitem.text()))
 
     def updateStatusBar(self, data):
         if data != "":