[analyzer] Fix UninitializedObjectChecker to not crash on uninitialized "id" fields

Differential Revision: https://reviews.llvm.org/D50673

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@339631 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed