GQ7: Don't publish 0,0 position

[Aposhian]

Is your feature request related to a problem? Please describe.
When the device first initializes, it starts publishing its location at 0,0 latitude longitude.

Describe the solution you'd like
Don't publish to ekf/llh_position if the filter is not initialized. It could still be appropriate to publish to odometry topics even if position doesn't exist yet, since those contain velocities and orientations as well.

This may be a feature to gate behind a parameter flag.

Describe alternatives you've considered
A downstream filter (in client application code) to filter out null positions from any calculations.

Additional context
While filter state and uncertainty are good measures to gate operation on, it would be nice to gate the actual data stream itself, because then it doesn't mess up tools that may not necessarily care about validation in general, but for which these outliers make life more difficult: i.e. analytics, visualizations, etc.