The background is :
The SmmMemoryAllocationLib of one of the instance of MemoryAllocation library class. As in MdePkg comment for AllocatePool() : “If AllocationSize is 0, then a valid buffer of 0 size is returned.”,the SMM library implements AllocatePool by SMST service SmmAllocatePool which does NOT support the zero size.
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@10171 6f19259b-4bc3-4df7-8a09-765794883524