Allow CreatedAt to be empty

https://git.debu.gs/gitweb/?p=fedibbs;a=commitdiff;h=fa5483ec4a2847b7e271938d1341530d1a927cf9
code, git.debu.gs | 2025-10-29 12:48:37 +0000 GMT | No.1637 
Allow CreatedAt to be empty

This fixes an issue where timelines cannot be viewed when one of the posts in the timeline has an empty/invalid timestamp. This fix is taken from bloat commit 3c221cd3746820fada38e8cc03e45184ebcecabd
  • [DH] pltypes.go