Do not set default values for lat and lon

Otherwise a location template is added with |0|0 coordinates (yeah! they
are valid) to each uploaded file if the user did not clear the input
fields that are hidden by default.

Can't set them to empty string, due to limtations in JsonSchema.
Setting them to null or empty string causes problems when editing
Campaign: pages

Regression introduced in 4a530c4b7341b9bb8409b194469f594f24fb5548

Bug: 51879
Change-Id: I1c3ddca19f36a7910f587a66f95b53d9facf4449
Merge "Do not set default values for lat and lon"