ROIPhiRZContainer::addROI can actually make two entries in the vector, if the ROI is close to +-pi. But if this happens. the length we've set for max_output in CaloClusterROIPhiRZContainerMaker::execute may be too small, leading to writes past the end of the vector. We print a warning in that case, but by then it's too late.
Resize max_output if needed, and remove the warning, since it can normally happen. (Leave it commented out for documentation.)
See ATLASRECTS-7160.