Fix the generic_response adapter

[mzimbres]

The generic_response adapter should not set an error in the result but let the caller check in each node whether an error occurred. Otherwise we cannot process responses to more than one request properly, like in the case of transactions.

The current implementation also has bug now since it might call result_->value() after an error has beed set in https://github.com/boostorg/redis/blob/46525371b9247a1ec208a6157880ec77f5ddadc4/include/boost/redis/adapter/detail/adapters.hpp#L101