Concatenated txxxxxx products aren't found when fname_format is set

When the filename format for concatenation is set differently from the (old) default format ({flying_unit_code}_{tile_name}_{polarisation}_{orbit_direction}_{orbit}_{acquisition_stamp}.tif), S1Tiling analysis of the final product already existing on disk fails to detect products done in a previous run.

# Here the calibration_type is used
fname_fmt.concatenation : {flying_unit_code}_{tile_name}_{polarisation}_{orbit_direction}_{orbit}_{acquisition_stamp}_{calibration_type}.tif

See the log that shows a search for:

s1tiling        - DEBUG    - check task_name: /home/luc/dev/S1tiling/tests/20200306-NR/data_out/33NVB/s1a_33NVB_vh_DES_007_20200108txxxxxx.tif
s1tiling        - DEBUG    - Checking concatenation product:
- /home/luc/dev/S1tiling/tests/20200306-NR/data_out/33NVB/s1a_33NVB_vh_DES_080_20200101txxxxxx.tif => ∅
- /home/luc/dev/S1tiling/tests/20200306-NR/data_out/33NVB/s1a_33NVB_vh_DES_080_20200101t045000_sigma.tif => ∅

instead of:

DEBUG - Checking concatenation product:
- /home/luc/dev/S1tiling/tests/20200306-NR/data_out/33NVB/s1a_33NVB_vh_DES_080_20200101txxxxxx_sigma.tif => ∃ (task)
- /home/luc/dev/S1tiling/tests/20200306-NR/data_out/33NVB/s1a_33NVB_vh_DES_080_20200101t045000_sigma.tif => ∅ (file)