Unlock the process lock when expand_name() fails, or we may leak the

process lock leading to a hang.  This bug was introduced in
kern_sig.c:1.351, when the call to expand_name() was moved earlier
bit this particular error case was not updated.

sys/kern/kern_sig.c

@@ -3063,6 +3063,7 @@ coredump(struct thread *td)
 
 	name = expand_name(p->p_comm, td->td_ucred->cr_uid, p->p_pid);
 	if (name == NULL) {
+		PROC_UNLOCK(p);
 #ifdef AUDIT
 		audit_proc_coredump(td, NULL, EINVAL);
 #endif