Reversion of withRangeStats

[tnixon]

I'm seeing failures of the withRangeStats function in recent testing. I've been testing the Financial services quickstart, and it fails at line 160: https://github.com/databrickslabs/tempo/blob/master/examples/financial_services_quickstart.py#L160

Failure is happening in the most recent build (v0.1.26), but doesn't fail on the version specified in the quickstart (v0.1.12) - so (it would appear) that a reversion has happened somewhere between these two builds that is causing the function to fail. Clearly this wasn't caught in our test code - so that will need to be updated along with a fix.