When the pattern for a regular expression is empty, every character
of the source is replaced with a copy of the "after" part of a
"QString::replace(re, after)". If input and output are huge this results
in a bad_alloc. We catch that here.
Fixes: QTCREATORBUG-16957
Change-Id: If512f407a2170d93ae7e4182219d9926945b14de
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>