<bugfix>Logging fails when Group executed by Map fails</bugfix>
<bugfix>Logging fails when Group executed by Map fails</bugfix>

The log controller tried to log the modules in the group that were
never executed. This failed and masked the real error.

core/log/controller.py:
- LogController.finish_group_execution:
  Skip if group.group_exec is not set
- LogController.finish_loop_execution:
  Skip if loop_exec is None

minesense/VisTrails,Nikea/VisTrails,VisTrails/VisTrails,minesense/VisTrails,VisTrails/VisTrails,minesense/VisTrails,minesense/VisTrails,hjanime/VisTrails,VisTrails/VisTrails,VisTrails/VisTrails,Nikea/VisTrails,Nikea/VisTrails,hjanime/VisTrails,celiafish/VisTrails,hjanime/VisTrails,celiafish/VisTrails,Nikea/VisTrails,celiafish/VisTrails,hjanime/VisTrails,celiafish/VisTrails,minesense/VisTrails,VisTrails/VisTrails,hjanime/VisTrails