test-command-template.t: make "age" filter test work on Feb 29th

reported by Julien Cristau.

--HG--
branch : stable
dispatch: handle empty `testedwith` value in extension

When extensions had an empty `testedwith` attribute the code tried to parse it
and failed. As a result the actual error were shallowed by a This crash.

We now treat empty strip as 'unknown'

--HG--
branch : stable
extra : rebase_source : d9fcf32fb439371106d26317c54755d0ff3a91a1