Fix error reporting of connect_timeout in libpq for value parsing

The logic was correctly detecting a parsing failure, but the parsing
error did not get reported back to the client properly.

Reported-by: Ed Morley
Author: Lars Kanis
Reviewed-by: Michael Paquier
Discussion: https://postgr.es/m/a9b4cbd7-4ecb-06b2-ebd7-1739bbff3217@greiz-reinsdorf.de
Backpatch-through: 12

src/interfaces/libpq/fe-connect.c

@@ -2025,7 +2025,11 @@ connectDBComplete(PGconn *conn)
 	{
 		if (!parse_int_param(conn->connect_timeout, &timeout, conn,
 							 "connect_timeout"))
+		{
+			/* mark the connection as bad to report the parsing failure */
+			conn->status = CONNECTION_BAD;
 			return 0;
+		}
 
 		if (timeout > 0)
 		{