Hi L1C - filter 0 and FILLVAL esa_energy_step data early

[subagonsouth]

Algorithm Description:

There are currently two places in the L1C code where esa_energy_step values of 0 or FILLVAL get filtered. Once when generating the empty PSET variables and once when computing exposure time. The code should be refactored to filter them out early. Probably right after the L1B data is read in.