Reset monacoLoading on failure

Fix
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/12198#note_37144070

app/assets/javascripts/repo/helpers/monaco_loader_helper.js

@@ -10,7 +10,10 @@ function repoEditorLoader() {
       Store.monaco = monaco;
       Store.monacoLoading = false;
       resolve(RepoEditor);
-    }, reject);
+    }, () => {
+      Store.monacoLoading = false;
+      reject();
+    });
   });
 }