update detector mask check depending on num of files
Initially attempted to fix this issue https://its.cern.ch/jira/browse/ATR-27021 with this MR !61173 (merged)
but created problems elsewhere
https://its.cern.ch/jira/browse/ATR-27061
https://its.cern.ch/jira/browse/ATR-27065
so trying to fix it.
The issue had to do with cases that more than 1 file was passed.
An offline ctest
failed, but seemed unrelated.
Edited by Aimilianos Koulouris