check for val->name == NULL when adding EDE text

check for val->name == NULL when adding EDE text

When a validator is being shut down, the associated name
`val->name` is set to NULL.  This could cause a crash if a worker
thread subsequently added an EDE code to the response containing
val->name in the extra text.

`validator_addede()` now checks whether the name is NULL before
trying to add it to the extra text.