message_edit: Fix error handling if user has re-narrowed.

static/js/message_edit.js

@@ -102,9 +102,11 @@ exports.save = function (row, from_topic_edited_only) {
             }
         },
         error: function (xhr, error_type, xhn) {
+            if (msg_list === current_msg_list) {
                 var message = channel.xhr_error_message("Error saving edit", xhr);
                 row.find(".edit_error").text(message).show();
             }
+        }
     });
     // The message will automatically get replaced when it arrives.
 };