When auto-generating pmns/domain.h files during PMDA Install,
for Perl PMDAs, if an earlier error occured these files may
exist but be empty. We can guard against this by regenerting
the files not only if they don't exist, but also if they're
empty - make it so.
When auto-generating pmns/domain.h files during PMDA Install,
for Perl PMDAs, if an earlier error occured these files may
exist but be empty. We can guard against this by regenerting
the files not only if they don't exist, but also if they're
empty - make it so.