Fix <rdar://problem/5987482> clang on xcode: null dereference in Sema::ActOnMemberReferenceExpr.

In addition to fixing the crasher, this commit fixes further improves property lookup (by searching protocols of qualified interfaces..."NSObject <prot>").


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@52001 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed