fix view file code-mirror bug (#6975)

frontend/src/components/file-view/file-toolbar.js

@@ -117,7 +117,7 @@ class FileToolbar extends React.Component {
     return (
       <Fragment>
         <div className="d-none d-md-flex justify-content-between align-items-center flex-shrink-0 ml-4">
-          {(fileType == 'PDF' && canDownloadFile ) && (
+          {(fileType == 'PDF' && canDownloadFile) && (
             <IconButton
               id="seafile-pdf-print"
               icon="print"

frontend/src/components/seafile-codemirror/index.js

@@ -23,17 +23,13 @@ class SeafileCodeMirror extends React.Component {
     readOnly: true,
   };
 
-  constructor(props) {
-    super(props);
-    this.options = null;
-  }
-
   onChange = (value) => {
     this.props.onChange && this.props.onChange(value);
   };
 
   render() {
     const { value, readOnly, fileExt } = this.props;
+    const extensions = [...getLanguageExtensions(fileExt).filter(item => item !== null)];
     return (
       <div className='seafile-code-mirror-container'>
         <CodeMirror
@@ -41,7 +37,7 @@ class SeafileCodeMirror extends React.Component {
           basicSetup={DEFAULT_CODEMIRROR_OPTIONS}
           theme={myTheme}
           readOnly={readOnly}
-          extensions={[...getLanguageExtensions(fileExt)]}
+          extensions={extensions}
           onChange={this.onChange}
         />
       </div>