bug: Do not forget a zeroconf channel if it doesn't confirm

[cdecker]

While debugging an issue on Greenlight, we found that one of the nodes
had forgotten a channel that it was waiting to confirm. This was caused by the "forget non-confirming channel" logic here:

lightning/lightningd/channel_control.c

Line 2007 in b5eef8a

log_unusual(channel->log,

The problem is that this code assumes that a channel that we aren't
funding cannot hold any funds that we own, hence we can forget the
channel without any issues. This used to be true until we introduced
zeroconf support. Now even unconfirmed channels may contain owned
funds, if they are zeroconf channels.

We need to adjust the logic to skip channels that are zeroconf && owned_sats > 0.

[cdecker]

I'm not quite sure why the check here isn't preserving the channel:

0dde74f

Ah, because it only considers funds we contributed to the funding, not our current owned funds.