Fix crash on zero-argument assignment operator.

Make sure we don't crash when checking whether an assignment operator
without any arguments is a special member.  <rdar://problem/14397774>.

llvm-svn: 186137
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 1c21b2c..0b79953 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -11535,7 +11535,8 @@
 
     CXXSpecialMember Member = getSpecialMember(MD);
     if (Member == CXXInvalid) {
-      Diag(DefaultLoc, diag::err_default_special_members);
+      if (!MD->isInvalidDecl())
+        Diag(DefaultLoc, diag::err_default_special_members);
       return;
     }