[PLG_COURSES_PROGRESS] fix scenario where sections with no members were generating a bad query
[PLG_COURSES_PROGRESS] fix scenario where sections with no members were generating a bad query

zweidner/hubzero-cms,zooley/hubzero-cms,zooley/hubzero-cms,zweidner/hubzero-cms,zooley/hubzero-cms,anthonyfuentes/hubzero-cms,anthonyfuentes/hubzero-cms,zweidner/hubzero-cms,anthonyfuentes/hubzero-cms,anthonyfuentes/hubzero-cms,zooley/hubzero-cms,zweidner/hubzero-cms