BUG/MINOR: listener: add an error check for unallocatable trash

Coverity noticed in issue #1416 that a missing allocation error was
introduced in tcp_bind_listener() with the rework of error messages by
commit ed1748553 ("MINOR: proto_tcp: use chunk_appendf() to ouput socket
setup errors"). In practice nobody will ever face it but better address
it anyway.

No backport is needed.
1 file changed