[analyzer] PR43551: Do not dereferce void* in UndefOrNullArgVisitor. Patch by Kristóf Umann! Differential Revision: https://reviews.llvm.org/D68591 git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@375329 91177308-0d34-0410-b5e6-96231b3b80d8