We had this assertion fail, and I can't see a clear reason why. Remove it
(i.e. don't crash because we're having trouble with creating invoice routehints)
and add logging.
```
Assertion failed: a->c->rr_number < b->c->rr_number (lightningd/invoice.c: cmp_rr_number: 623)
lightningd: FATAL SIGNAL 6 (version v0.10.2-modded)
0x5654f1c40061 send_backtrace
common/daemon.c:33
0x5654f1c400e9 crashdump
common/daemon.c:46
0x7efd87da6c8a ???
???:0
```
There are several possible causes for this:
1. We have two channels with the same rr_number. A quick audit shows we always set that rr_number to a unique value (and 64 bits, so wrap is not possible between the release and now!).
2. It's theoretically possible that sort() could compare a value with itself, but that would be really dumb: it doesn't that I've ever seen, but then, we've never seen this assert() hit, either.
3. listincoming has given us the same channel twice. I don't see how that is possible: we had a race where channels could momentarily vanish, but never be duplicated (emailed crash.log shows no duplicates!).
4. General corruption/freed memory access. If a channel we've just looked up is gone but still in the hash table, this is possible but would cause lots of random behavior and crashes.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
3a61e0e181