routing: populate the chain filter before calling syncGraphWithChain
routing: populate the chain filter before calling syncGraphWithChain

In this commit we fix an existing bug within the ChannelRouter. Before
this commit, we would sync our graph prune state, *then* update the
cain filter. This is incorrect as the blocks we manually pruned may
have included channel closing transactions. As a result, we would miss
the pruning of a set of channels, and assume that they were still
active.

In this commit, we fix this by reversing the order: we first update the
chain filter and THEN sync the channel graph.

LightningNetwork/lnd,aakselrod/lnd,LightningNetwork/lnd,aakselrod/lnd