…to fix/tsm-out-of-range-index

As the Len function is used as part of the parseSeriesKey, this also needs to be accounted for on the nil return from this function as it is used in different contexts

In both sections for index.go there is a pre-existing length check against the series key which should catch invalid values, perhaps this explains why it hasn't cropped up in the reported panics. For even more safety, we can also skip a nil key because we know that subsequent calls will cause a panic where this key is attempted to be used

A key with no tags is valid, so we should not check for BOTH nil key and tags as a key could be nil, which is invalid, yet still have tags and therefore cause the check to pass which we do not want

Prior to this, the else was always defaulted to at the end of the conditional branch, which causes unexpected behaviour and a failure of a bunch of tests.

In a recent change to this, we agreed on a simple name == nil check for the actual data. As a follow on to this, I just realised that we don't actually want to nil back the tags, even if they're not checked, because having no tags is a valid input so we can simply return whatever we were passed unchanged.

…data/influxdb into fix/tsm-out-of-range-index

…data/influxdb into fix/tsm-out-of-range-index