usercss: don't relint on save; mode is an object once initialized

edit/lint.js

@@ -32,10 +32,8 @@ var linterConfig = {
   getName() {
     // some dirty hacks to override editor.linter getting from prefs
     const linter = prefs.get('editor.linter');
-    if (linter && editors[0] && editors[0].getOption('mode') !== 'css') {
+    const mode = linter && editors[0] && editors[0].doc.mode;
-      return 'stylelint';
+    return mode && mode !== 'css' && mode.name !== 'css' ? 'stylelint' : linter;
-    }
-    return linter;
   },
 
   getCurrent(linter = linterConfig.getName()) {

edit/source-editor.js

@@ -59,10 +59,16 @@ function createSourceEditor(style) {
 
   function initLinterSwitch() {
     const linterEl = $('#editor.linter');
+    let prevMode = NaN;
     cm.on('optionChange', (cm, option) => {
       if (option !== 'mode') {
         return;
       }
+      const mode = cm.doc.mode;
+      if (mode === prevMode || mode && mode.name === prevMode) {
+        return;
+      }
+      prevMode = mode;
       updateLinter();
       update();
     });