Ensure that there are enough elements for a direction computation.
requested to merge goetz/athena:ATLASRECTS-7363_22.0_fix_division_by_zero_in_TRT_TrackExtensionTool_xk into 22.0
Ensure that there are at least two elements on the road to compute the initial direction. This prevents a possible division by zero.
Closes ATLASRECTS-7363