There was a Flow anti-corruption check to prevent software that does not understand content model from creating Flow boards incorrectly: https://gerrit.wikimedia.org/r/#/c/330624/

However, I have to revert it, since it prevents empty (corrupt but with no actual content) boards from being visited.

Without it, the board can be visited (and appears blank), and is postable.

However, after the corrupt boards are fixed, this should be put back, to prevent other potential (unknown) causes of this kind of corruption.

Checklist:

• T154623: Workflow ID null for some user talk pages on gomwiki
• FlowFixInconsistentBoards.php --dry-run like P4715 , to verify there are no corrupt pages
• Revert https://gerrit.wikimedia.org/r/#/c/357445/ (Revert "Throw when unserializing invalid Flow workflow metadata JSON").