channeld: don't forget channels that we've put funds into

Typically we forget a channel if 2016 blocks have passed and
the funding transaction hasn't been mined yet, however we
SHOULD NOT forget these channels if we've got funds in them!

lightningd/channel_control.c

@@ -773,6 +773,10 @@ is_fundee_should_forget(struct lightningd *ld,
 	if (block_height - channel->first_blocknum < max_funding_unconfirmed)
 		return false;
 
+	/* If we've got funds in the channel, don't forget it */
+	if (!amount_sat_zero(channel->our_funds))
+		return false;
+
 	/* Ah forget it! */
 	return true;
 }