Prevent duplicate waddrmgr lock error.

Fixes #270.

wallet/wallet.go

@@ -611,6 +611,7 @@ out:
 
 		// Select statement fell through by an explicit lock or the
 		// timer expiring.  Lock the manager here.
+		if timeout != nil {
 			timeout = nil
 			err := w.Manager.Lock()
 			if err != nil {
@@ -619,6 +620,7 @@ out:
 				w.notifyLockStateChange(true)
 			}
 		}
+	}
 	w.wg.Done()
 }