Bug 1561577 - prevent default when esc is pressed on shortcutsModal r=jlast

Prevent toggling open Split Console with escape is pressed to toggle shortcutsModal closed.

Differential Revision: https://phabricator.services.mozilla.com/D36448

--HG--
extra : moz-landing-system : lando

devtools/client/debugger/src/components/App.js

@@ -166,6 +166,7 @@ class App extends Component<Props, State> {
     }
 
     if (shortcutsModalEnabled) {
+      e.preventDefault();
       this.toggleShortcutsModal();
     }
   };