[libpng16] ci: Verification should pass regardless of autoconf artifacts

Allow ci_verify_configure.sh to pass regardless whether the configure
script and the associated configure control files are present.
This is necessary for the branches newer than 'libpng16', where these
artifacts are no longer auto-generated by default.

This is a cherry-pick of commit 09ec97edc099538d548a67253b990660c912af4f
from branch 'libpng18'.
1 file changed