Android: Fix crash in String.replace() in release builds

When enabling optimizations in the compiler, it produces bogus
code for the regExp->value deref in the line

nMatchOffsets += regExp->value->captureCount() * 2

This is a random refactoring to work around the compiler bug.
The only line that actually needs to be touched is the one mentioned
above, but I replaced all uses of regExp->value so that it
wouldn't look too weird.

Task-number: QTBUG-38692
Change-Id: Ib33a523a86ce51ebc6c7095a803fedaebcaa8e63
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>