If the scan for quick tests was triggered just by a change of a
qml file (including indexing by the respective modelmanager) we
might find tests that won't be able to execute.
If we have already found quick tests we know their respective
project files. If we cannot find the files to be scanned inside the
already found ignore scan requests for such files.

This patch is kind of a continuation of b570ee1b


(Fix initial parsing when loading session)

Change-Id: Ic1228641f60abf127134acbd4232a0ddd30ef159
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>