Update zlib from 1.2.12 to 1.2.13
1.2.13 has a security fix, which alone is a good reason to update.
But I'm also hoping it will fix this UBSan warning from the VTK::IOImageCxx-TestNIFTIReaderWriter
test: ThirdParty/zlib/vtkzlib/gzlib.c:431:23: runtime error: applying zero offset to null pointer
Edited by Sean McBride