...by avoiding calls to parentStmt, thereby also improving the precision of
exactly which comma operators to ignore (which turned up a handful more finds).
Also added tests.

Change-Id: Ie74f824fd7f54131aab09b59086452fb4f3ff827
Reviewed-on: https://gerrit.libreoffice.org/43181Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>