Parsoid: Use fall-back for 421s too
Parsoid: Use fall-back for 421s too

Parsoid/PHP will emit 421s if we provide it with data-parsoid belonging
to Parsoid/JS. While this should never happen, ensure that the fall-back
is in place to keep our sanity.

Bug: T237563

wikimedia/mediawiki-services-restbase,Pchelolo/restbase,cscott/restbase,d00rman/restbase,d00rman/restbase,cscott/restbase,Pchelolo/restbase,milimetric/restbase,wikimedia/restbase,wikimedia/mediawiki-services-restbase,wikimedia/restbase,milimetric/restbase