[BASOP CI] Fix in tests/cmp_pcm.py for differing file lengths -- JBM
Fix in tests/cmp_pcm.py for differing file lengths, which e.g. occurs in JBM tests.
The current scripts do not output any MLD nor MAXIMUM ABS DIFF values when the output length differs. This fixes the parsing error by outputting None for these values. The result in the pytest and mld.csv is however the same.