Prevent duplicate waddrmgr lock error.
Prevent duplicate waddrmgr lock error.

Fixes #270.

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