Fix: only load task once for building
Fix: only load task once for building

- Fixes a bug in which a geometry tile task was sent to worker again when its dependent rasters were
not initially loaded and attemped to load the next iteration.
Now there should not be any duplicate tasks sitting the the tileworker queue

tangrams/tangram-es,tangrams/tangram-es,cleeus/tangram-es,tangrams/tangram-es,cleeus/tangram-es,cleeus/tangram-es,quitejonny/tangram-es,quitejonny/tangram-es,cleeus/tangram-es,quitejonny/tangram-es,quitejonny/tangram-es,cleeus/tangram-es,tangrams/tangram-es,cleeus/tangram-es,tangrams/tangram-es,quitejonny/tangram-es,tangrams/tangram-es,quitejonny/tangram-es,tangrams/tangram-es