fixed execution on fake tx

Author: asmyasnikov

internal/table/conn/conn.go

@@ -473,6 +473,8 @@ func (c *Conn) beginTx(ctx context.Context, txOptions driver.TxOptions) (tx curr
 		return nil, xerrors.WithStackTrace(err)
 	}
 
+	c.currentTx = tx
+
 	return tx, nil
 }
 
@@ -482,7 +484,5 @@ func (c *Conn) BeginTx(ctx context.Context, txOptions driver.TxOptions) (driver.
 		return nil, xerrors.WithStackTrace(err)
 	}
 
-	c.currentTx = tx
-
 	return tx, nil
 }