QTestlib: Re-enable Windows error dialog when -nocrashhandler is passed.

The error dialog is sometimes desired when trying to attach a
debugger. Use the  -nocrashhandler option for it, which already
exists on UNIX.

Change-Id: I42c9311242cdeaa81a148af9bf61875e1bc6f32c
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>