Make sure the path we add to pendingDocs is canonical

Otherwise i had a problem where we were waiting for
 /usr/share/unity8//Dash/DashPageHeader.qml
but then on QmlProfilerDetailsRewriter::documentReady we got
 /usr/share/unity8/Dash/DashPageHeader.qml
and since it's not the same qstring we didn't realize it was the same file

Task-number: QTCREATORBUG-16020
Change-Id: I3b07450438d98734fbbff9f8b7a3d9d851ed4e5d
Reviewed-by: Ulf Hermann <ulf.hermann@theqtcompany.com>