Take into account the segwit tx header when...

Take into account the segwit tx header when...
...selecting coins

We take into account the larger segwit tx header for every
transaction, not just the segwit ones. The reason for this is that
we prefer to overestimate the fees for the transaction than
underestimating them - the former might create txs with a slightly
higher feerate than the requested one, while the latter might
create txs with a slightly lower one - or worse, invalid (<1 sat/vbyte)!