Fix crash in MuonClusterSegmentFinderTool

This MR fixes a problem that was accidentally introduced by !30045 (merged) . Previously the MuonClusterSegmentFinderTool retrieved a vector of ROT pointers that had been cached on the MuonSegment. When this vector was constructed, a check for successful casts from MeasurementBase to RIO_OnTrack was performed, and failed casts were skipped. In the previous MR, this cached vector was removed for thread-safety reasons, but I neglected to include a check for failed casts in the changes to MuonClusterSegmentFinderTool, leading to a crash. This fixes the problem by building a vector of ROT pointers, with a check for failed casts, locally in MuonClusterSegmentFinderTool, and then using this in the loop over the segment hits.