[#667] Fix data for map on Akvo at a glance page

The live database has two projects with a primary_location field that is
set, but the location object is not present in the DB.

Fix by adding a filter that removes projects without a valid primary
location object.
Merge pull request #668 from akvo/hotfix/667_data_overview

[#667] Fix data for map on Akvo at a glance page