dcmtk expects monotonically increasing SegmentNumber

[razorx89]

Currently, only segments with a positive mask get copied to the SegmentSequence:

pydicom-seg/pydicom_seg/writer.py

Lines 165 to 170 in ee1aba7

	writer_utils.copy_segmentation_template(
	target=result,
	template=self._template,
	segments=labels_to_process,
	skip_missing_segment=self._skip_missing_segment,
	)

However, the DICOM standard says "Segment Number (0062,0004) shall be unique within each Instance, start at a value of 1, and increase monotonically by 1.". Dcmtk correctly enforces this and throws an error.