OpenEXR's CompositeDeepScanLine integer-overflow leads to heap OOB write

SummaryFunction: CompositeDeepScanLine::readPixels, reachable from high-level multipart deep read flows MultiPartInputFile + DeepScanLineInputPart + CompositeDeepScanLine.Vulnerable lines src/lib/OpenEXR/ImfCompositeDeepScanLine.cpp:- totalsizesptr += countsjptr; line 511- overallsamplecount +=...