[CF 5749] Fix PQport to never return NULL if the connection is valid

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https://commitfest.postgresql.org/patch/5749

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Patch(es): https://www.postgresql.org/message-id/CA+mi_8aaQdULFYo6jDtG+aUzfNmyuitrqNAhx_N_BrCu-beeCw@mail.gmail.com
Author(s): Daniele Varrazzo

Author: Commitfest Bot

src/interfaces/libpq/fe-connect.c

@@ -7536,7 +7536,9 @@ PQport(const PGconn *conn)
 	if (!conn)
 		return NULL;
 
-	if (conn->connhost != NULL)
+	if (conn->connhost != NULL &&
+		conn->connhost[conn->whichhost].port != NULL &&
+		conn->connhost[conn->whichhost].port[0] != '\0')
 		return conn->connhost[conn->whichhost].port;
 
 	return "";