Bug 1913061 - [devtools] Fix crash when no editor and no next selected source r=devtools-reviewers,nchevobbe

Differential Revision: https://phabricator.services.mozilla.com/D220086

devtools/client/debugger/src/components/Editor/index.js

@@ -141,7 +141,11 @@ class Editor extends PureComponent {
   UNSAFE_componentWillReceiveProps(nextProps) {
     let { editor } = this.state;
 
-    if (!editor && nextProps.selectedSource) {
+    if (!editor) {
+      // See Bug 1913061
+      if (!nextProps.selectedSource) {
+        return;
+      }
       editor = this.setupEditor();
     }