Check for nil to prevent panic.
Check for nil to prevent panic.

ok jrick@

synrg-labs/btcwallet,synrg-labs/btcwallet,decred/dcrwallet,Stash-Crypto/btcwallet,jrick/btcwallet,Roasbeef/btcwallet,btcsuite/btcwallet,jrick/dcrwallet,jrick/dcrwallet,jrick/btcwallet,btcsuite/btcwallet,Roasbeef/btcwallet,decred/dcrwallet,Stash-Crypto/btcwallet