Stem should mark relays as "is_unmeasured" if the "measured" property is not set
When fetching a consensus vote - e.g. using the stem.descriptor.remote.DescriptorDownloader.get_vote method, relays that have not been measured will not have a "Measured" entry in their "w Bandwidth" lines, which is slightly different than the consensus, which will say "Unmeasured". So, the is_unmeasured parameter will not be correctly set to True, whereas the measured parameter will be None.