Fix "0" Perl version in cpanstats.perl

[preaction]

Some of the test summary data has "0" where a Perl version should be. We need to either figure out the correct version for these reports, or delete them: Referential integrity will not allow these reports to exist, and they are useless if we can't figure out what Perl version they are for.

Find these data with: select * from cpanstats where cpanstats.perl = "0".

None of these 2294 rows are more recent than 2010-07-02, so even if we must get rid of them we aren't losing much. Some of them are for OSes or platforms that I'm not sure we have access to anymore, which is valuable, so we should still try to save this data.