LibGUI: Bubble up Key_Escape if no hook is plugged in TextEditor

The TextEditor widget was always accepting the Key_Escape event even if
the `on_escape_pressed` was empty. In other words, it was discarding the
event.

This behavior prevented shortcuts to be activated at a higher level.

Userland/Libraries/LibGUI/TextEditor.cpp

@@ -1077,6 +1077,8 @@ void TextEditor::keydown_event(KeyEvent& event)
     if (event.key() == KeyCode::Key_Escape) {
         if (on_escape_pressed)
             on_escape_pressed();
+        else
+            event.ignore();
         return;
     }