If both the 'other' and 'current' declarations are implicit, we don't
emit a diagnostic unless they are both derived from property wrappers
or lazy property storage.
However, we would still call setInvalid() unconditionally, which splats
an ErrorType into the interface type, which would crash in the AST
verifier if no other diagnostic was emitted.
Fixes <rdar://problem/67259506>.
