also make the plugin ignore the case where we have var decl's in the
clause we want to flatten, which could lead to problematic extension of
variable lifetime

Change-Id: I3061f7104e8c6a460bf74f5eac325a516ec50c59
Reviewed-on: https://gerrit.libreoffice.org/42889Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>