We use feerate in several places, and each one really should react
differently when it's not available (such as when bitcoind is still
catching up):
1. For general fee-enforcement, we use the broadest possible limits.
2. For closingd, we use it as our opening negotiation point: just use half
the last tx feerate.
3. For onchaind, we can use the last tx feerate as a guide for our own txs;
it might be too high, but at least we know it was sufficient to be mined.
4. For withdraw and fund_channel, we can simply refuse.
Fixes: #1836
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Rusty Russell
175db926c2