Fix infinite loop in MIME classinfo parser in ActiveQt

This is the same change as dd0feaa9

 but
done in the other location where the same loop is handled in the same
manner.

Change-Id: I86773b1ed5c9ac7bd23974e9eefcb89f7b515014
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>