Fix bug in syncing to address index

An ErrSyncToIndex error when calling SyncAccountToAddrIndex simply
indicates that the address manager is ahead of the address pool
index, which is not an error causing any issues. This error is now
caught and skipped.

Fixes #174.

wallet/sync.go

@@ -475,10 +475,16 @@ func (w *Wallet) rescanActiveAddresses() error {
 				_, err := w.Manager.SyncAccountToAddrIndex(acct,
 					addressPoolBuffer, branch)
 				if err != nil {
-					return fmt.Errorf("failed to create initial waddrmgr "+
-						"address buffer for the address pool, "+
-						"account %v, branch %v: %s", acct, branch,
-						err.Error())
+					// A ErrSyncToIndex error indicates that we're already
+					// synced to beyond the end of the account in the
+					// waddrmgr.
+					errWaddrmgr, ok := err.(waddrmgr.ManagerError)
+					if !ok || errWaddrmgr.ErrorCode != waddrmgr.ErrSyncToIndex {
+						return fmt.Errorf("failed to create initial waddrmgr "+
+							"address buffer for the address pool, "+
+							"account %v, branch %v: %s", acct, branch,
+							err.Error())
+					}
 				}
 			}