[analyzer] Enhance the member expr tracking to account for references.

As per Jordan's suggestion. (Came out of code review for r163261.)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@163269 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/StaticAnalyzer/Checkers/DereferenceChecker.cpp b/lib/StaticAnalyzer/Checkers/DereferenceChecker.cpp
index 45f4036..45d854b 100644
--- a/lib/StaticAnalyzer/Checkers/DereferenceChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/DereferenceChecker.cpp
@@ -130,7 +130,7 @@
   }
   case Stmt::MemberExprClass: {
     const MemberExpr *M = cast<MemberExpr>(S);
-    if (M->isArrow()) {
+    if (M->isArrow() || bugreporter::isDeclRefExprToReference(M->getBase())) {
       llvm::raw_svector_ostream os(buf);
       os << "Access to field '" << M->getMemberNameInfo()
          << "' results in a dereference of a null pointer";