E3-1536: Fix cell arg with no active environment
If no environment has been activated, EPICS_DRIVER_PATH will not be set. This case is now handled a bit more carefully, in that the cell path(s) instead will be used.
If no environment has been activated, EPICS_DRIVER_PATH will not be set. This case is now handled a bit more carefully, in that the cell path(s) instead will be used.