BinaryJedis.multi(TransactionBlock) should not call discard when exception occurred

* In BinaryJedis.multi(TransactionBlock), multi & exec already fired before exception occured, so sending discard has no effect, and made another error
** add unit test (error inside TransactionBlock)
*** Transaction with error - Redis discards transaction automatically (execabort)
*** Transaction with error - Redis doesn't roll back (force to execute all)