Treat fstat(2) failure (different than EBADF) as fatal error.

Reported by:	Mikolaj Golub <to.my.trociny@gmail.com>
MFC after:	1 week

sbin/hastd/hastd.c

@@ -188,6 +188,7 @@ descriptors_assert(const struct hast_resource *res, int pjdlogmode)
 			snprintf(msg, sizeof(msg),
 			    "Unable to fstat descriptor %d: %s", fd,
 			    strerror(errno));
+			break;
 		}
 		if (fd == STDIN_FILENO || fd == STDOUT_FILENO ||
 		    fd == STDERR_FILENO) {