Pipeline incorrectly calls DISCARD after EXEC in case of EXECABORT error

[nickgaya]

Version:
Redis-py 3.4.1
Redis 5.0.7

Platform:
Python 3.8.2
Mac OS 10.13.6

Description:
Executing an explicit transaction containing an invalid command results in a response error, masking the original parsing error.

Example:

from redis import Redis
redis = Redis(...)

with redis.pipeline() as pipe:
    pipe.multi()
    pipe.execute_command('INCR', 'a', 'b', 'c')
    pipe.execute()

Expected:

redis.exceptions.ResponseError: Command # 1 (INCR a b c) of pipeline caused error: wrong number of arguments for 'incr' command

Actual:

redis.exceptions.ResponseError: DISCARD without MULTI

[andymccurdy]

Merged in 07fec7e