Not totally sure, but seems like we need to set the error with the
evaluated ModifierData?
I havent hunted this down to a single commit, but assume this broke with
the activity around T58210:
rB71e2efc4ce6b
rB484389cdcd6c
rBde491abf9962
rB989fbff16f49
Alternative would be to use BKE_Report (see DataTransfer modifier), but
this just gets the message back from 'surfacedeformBind' to
'surfacedeformModifier_do' to set the error on the evaluated modifier data
there.