*8190* fix URL encoding for DOIs

Typo/thinko on my part. Adapting it to include suffix part. Something like this? (It still might be overly permissive, but should work OTOH)
preg_match('/^\d+(\.\d+)+\//', $doi)
This will match the prefix specifically, including subdivisions, and ensure that there's a trailing slash. The suffix will follow that, but isn't matched as part of the regexp.