Fix a crash-on-invalid.

Much to everyone's surprise, the default constructor for TypeResult produces
an instance with Invalid == false. This seems like a decision we may want to
revisit.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@138601 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Sema/SemaTemplate.cpp

@@ -2131,7 +2131,7 @@ TypeResult Sema::ActOnTagTemplateIdType(TagUseKind TUK,
   
   QualType Result = CheckTemplateIdType(Template, TemplateLoc, TemplateArgs);
   if (Result.isNull())
-    return TypeResult();
+    return TypeResult(true);
   
   // Check the tag kind
   if (const RecordType *RT = Result->getAs<RecordType>()) {

test/SemaTemplate/missing-class-keyword-crash.cpp

@@ -0,0 +1,7 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+class G {};
+template <Foo> // expected-error{{unknown type name 'Foo'}} \
+               // expected-note{{template parameter is declared here}}
+class Bar {};
+
+class Bar<G> blah_test; // expected-error{{template argument for non-type template parameter must be an expression}}