CID 357292: Improper use of negative value in lib/isc/netmgr/tcp.c

Coverity Scan reports the following on main:

*** CID 357292:    (REVERSE_NEGATIVE)
/lib/isc/netmgr/tcp.c: 309 in isc_nm_tcpconnect()
303     
304     	atomic_store(&sock->active, true);
305     
306     	result = tcp_connect_direct(sock, req);
307     	if (result != ISC_R_SUCCESS) {
308     		atomic_store(&sock->active, false);
>>>     CID 357292:    (REVERSE_NEGATIVE)
>>>     You might be using variable "sock->fd" before verifying that it is >= 0.
309     		if (sock->fd != (uv_os_sock_t)(-1)) {
310     			isc__nm_tcp_close(sock);
311     		}
312     		isc__nm_connectcb(sock, req, result, true);
313     	}
314     

Seems to originate in fffd4444.