Fix TO Go CRConfig to omit null missLocations

[rob05c]

This fixed the Golang CRConfig to do what Perl does: omit the missLocation field if it's null in the database.

Specifically, the Go MissLocation field is omitempty, but was always being assigned an object ( MissLocation: &tc.CRConfigLatitudeLongitudeShort{}). This changes it to only assign an object if the miss location exists.

This also warns if Lat or Lon is set, but not both. This is different from Perl, which would put whichever was set in the CRConfig. It's never useful to have Lat without Lon, so IMO that should be considered a bug, and warned, which this does.

Long term, we should make it impossible in the DB and UI to set Lat without Lon. But that's a bigger change.

[asfgit]

Refer to this link for build results (access rights to CI server needed):
https://builds.apache.org/job/incubator-trafficcontrol-PR/1510/
Test PASSed.