QML Preview: Keep showing the last good state if intermediate typing results in a broken QML document

Code

import QtQuick

Window {
    width: 400
    height: 300
    visible: true
}

Steps to test

1. Put the code above in a QML project and start the QML Preview
2. Add a new import, like import QtQuick.Controls
3. Add a new property, like color: 'green'

Current outcomes

• (Step #2): Typing "import " is fine. But as soon as we add another character ("import Q"), the window disappears and the General Mesages pane shows an error ("module "Q" is not installed")
• (Step #3): Typing "color: " is fine. But as soon as we hit the quotation-mark key ("color: ''"), the window disappears and the General Mesages pane shows an error ("Invalid property assignment: color expected")

Suggestion
If an attempt to load an updated QML document fails, then the previous good preview should be retained