gossip_store: fix 'bad node_announcement' by allowing node_announcement on un-updated channel.

When we first receive a channel_update, we write both the
channel_announcement and that channel_update to the store: we need
that first update so we can set the channel_announcement timestamp.

However, the channel_update can be replaced later.  This means we can
have a channel_announcement, a node_update which relies on it, then
the channel_update later.

So move the "this applies to a pending announcement" check lower, where
gossip_store can use it too.  Has a nice side-effect of avoiding
one lookup of the node id.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

tests/test_gossip.py

@@ -1132,7 +1132,6 @@ def test_gossip_store_load_complex(node_factory, bitcoind):
     wait_for(lambda: l2.daemon.is_in_log('gossip_store: Read '))
 
 
-@pytest.xfail(strict=True)
 @unittest.skipIf(not DEVELOPER, "need dev-compact-gossip-store")
 def test_gossip_store_compact(node_factory, bitcoind):
     l2 = setup_gossip_store_test(node_factory, bitcoind)