QRegExp matching methods modify the object, which we don't want to. In
particular, when we receive a QRegExp from the user or we store in a
context that might require thread-safety, make sure we make a copy
before using it.
QRegularExpression has no such shortcoming.
Task-number: QTBUG-25064
Change-Id: I6b2d2530238a7e04b44859664a2962f2f466ee30
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>