llvm-undname: Fix an assert-on-invalid, found by oss-fuzz

If a template parameter refers to a pointer to member, but the mangling
of that was a string literal instead of a real symbol, llvm-undname used
to crash instead of rejecting the input.

llvm-svn: 361402

Author: nico

llvm/lib/Demangle/MicrosoftDemangle.cpp

@@ -2175,8 +2175,10 @@ Demangler::demangleTemplateParameterList(StringView &MangledName) {
       SymbolNode *S = nullptr;
       if (MangledName.startsWith('?')) {
         S = parse(MangledName);
-        if (Error)
+        if (Error || !S->Name) {
+          Error = true;
           return nullptr;
+        }
         memorizeIdentifier(S->Name->getUnqualifiedIdentifier());
       }
 

llvm/test/Demangle/invalid-manglings.test

@@ -169,3 +169,8 @@
 ; CHECK-EMPTY:
 ; CHECK-NEXT: ??_C@_12@?z
 ; CHECK-NEXT: error: Invalid mangled name
+
+??$foo@$1??_C@_02PCEFGMJL@hi?$AA@@
+; CHECK-EMPTY:
+; CHECK-NEXT: ??$foo@$1??_C@_02PCEFGMJL@hi?$AA@@
+; CHECK-NEXT: error: Invalid mangled name