Improvements to NULL geom handling

[hannahkates]

Current issues with NULL geom handling:

1. To provide more context to issue Records with no geometry map to 0,0 #44 , currently the app only checks whether the table's first row has a null geom and then assumes 0,0 for the geom of all records rather than checking through the rest of the records which may have valid geometries.

2. If there is a null geom further down in the table, the query throws an error "must start with number, buffer, array or string"

App could default to only showing records where geom is not null -- or find a better way to still include the null geom records in the table but not render them on the map. Maybe the rendering component could always default to include "where geom is not null."