No length check on pubKeys in Eth2FastAggregateVerify

[dnkolegov]

Description

There is no length check on pubKeys slice in Eth2FastAggregateVerify - https://github.com/prysmaticlabs/prysm/blob/develop/crypto/bls/blst/signature.go#L135.

If pubKeys is nil or empty and s is not G2_POINT_AT_INFINITY the function returns result of s.innerFastAggregateVerify(pubKeys, msg). The last function doesn't validate pubKeys.

The spec says that Eth2FastAggregateVerify should return the result of FastAggregateVerify, instead of this innerFastAggregateVerify will be called.

[nisdas]

Thanks for the report @dnkolegov , it was previously split out to prevent some redundant calls from being made, but it has been reverted back in #9742 to be more inline with the spec.