QML editor does not display error messages until further error is added

1. Open the attached file:

   import QtQuick 2.3
   
   Rectangle {
       Timer {
           onTriggered:
       }
   
       MouseArea {
       }
   }
   

   The first closing curly brace is underlined because it is unexpected. There is no inline error message, though.

2. Type something inside the curly braces of the MouseArea.
   Now the error message "Unexpected Token" will appear next to "onTriggered".

This error message should already be displayed when opening the file.

Found while testing for QTCREATORBUG-15680.