Avoid matching names like ._IMAT_Flower_Flat_Before_000000.tif

[samtygier-stfc]

Summary

We have a dataset that has some garbage files with names like ._IMAT_Flower_Flat_Before_000000.tif. These are possibly caused during an interrupted file copy.

#1878 made the file pattern matching a lot less strict, so we now pick up these files as candidates for the flat and dark. We should probably ignore any file starting with a . as those are very unlikely to be actual valid data files.

Steps To Reproduce

Make a copy of a dataset, eg IMAT00010675
In the Flat_Before make some problem files
for f in *.tif ; do touch ._${f} ; done
In MI do Load Dataset
Select the sample from the Tomo directory
Note that ._IMAT_Flower_Flat_Before_000000.tif is picked up as the Flat Before
Load and note the error message

Expected Behaviour

Files starting with a . should not be picked automatically

Context

Probably introduced by #1878