readImageDicomFileSeries doesn't read segmentation dicom correctly

When using `readImageDicomFileSeries` for reading a multiframe dicom file of SOP class = 1.2.840.10008.5.1.4.1.1.66.4 which is Segmentation modality.
The file is read but with incorrect spacing and image dimensions. I suspect that it doesn't find the pixel spacing in the dicom tags (even though the info is present in the dicom tags), hence it defaults to `spacing = [1, 1, 1]` and also does not reconfigure the frames into fewer z-slices based on number of unique labels (for e.g. number of frames = number of labels * expected z-slices).

Since `readImageDicomFileSeries` uses gdcm as backend, this could be a fix for gdcm.

Test data: https://data.kitware.com/#user/61d87b684acac99f42cd366c/folder/654d0c3dfdc1508d8bec1baf
Expected image size: [512, 512, 134], spacing: [0.9765625, 0.9765625, 3]
Actual image size: [512, 512, 536], spacing: [1, 1, 1]