Fix repeated images when channels are in separate files

[tddough98]

I'm running MERlin with each channel in a separate file and with two channels per round. For example, bits 1 and 2 are measured in round 0 and are stored in example_v0_t0_c0_nbit1.tif and example_v0_t0_c1_nbit9.tif. However, the images from the second file for bit 9 are never loaded while the images for bit 1 are loaded twice.

Curiously, the images for bit 1 are loaded for bits 1 and 2 instead of bits 1 and 9 (and bit 2 is loaded as bit 3 and 4, and so on).

[tddough98]

incorrect data organization .csv was causing bit 1 to be used for bits 1 and 2 instead of bits 1 and 9, but repeating the image remains an issue

[tddough98]

when channels for the same imaging round and fov are stored in separate files, the fileMap will have multiple files for a given type, round, and fov, but silently uses the first one and ignores the rest