Fix incorrect assertion in libpqwalreceiver

Was supposed to check the length of the array, but was checking its
size in bytes.

Author: Jacob Brazeal <jacob.brazeal@gmail.com>
Discussion: https://www.postgresql.org/message-id/CA%2BCOZaA_9afJxj9ZuO73U5P7WXP%2BZM9NGnZvTDCmBFz0FGP%2BwA@mail.gmail.com

src/backend/replication/libpqwalreceiver/libpqwalreceiver.c

@@ -208,7 +208,7 @@ libpqrcv_connect(const char *conninfo, bool replication, bool logical,
 	keys[++i] = NULL;
 	vals[i] = NULL;
 
-	Assert(i < sizeof(keys));
+	Assert(i < lengthof(keys));
 
 	conn = palloc0(sizeof(WalReceiverConn));
 	conn->streamConn = PQconnectStartParams(keys, vals,