Initialize `ConceptReference` of new `AutoTypeLoc` with nullptr.

[sammccall]

Days since learning something new and horrifying about TypeLoc: zero

You might consider deleting the '= nullptr' from AutoTypeLocInfo::CR since it appears we never actually run the constructors/destructors of TypeLocInfo classes (at least when using TypeLocBuilder).

clang/lib/Sema/TreeTransform.h

Result = getDerived().RebuildAutoType(NewDeduced, T->getKeyword(), NewCD,
                                           NewArgList);
     if (Result.isNull())
       return QualType();
   }
 
   AutoTypeLoc NewTL = TLB.push<AutoTypeLoc>(Result);
   NewTL.setNameLoc(TL.getNameLoc());
   NewTL.setRParenLoc(TL.getRParenLoc());
+  NewTL.setConceptReference(nullptr);
 
   if (T->isConstrained()) {
     DeclarationNameInfo DNI = DeclarationNameInfo(
         TL.getTypePtr()->getTypeConstraintConcept()->getDeclName(),
         TL.getConceptNameLoc(),
         TL.getTypePtr()->getTypeConstraintConcept()->getDeclName());
     auto *CR = ConceptReference::Create(
         SemaRef.Context, NewNestedNameSpec, TL.getTemplateKWLoc(), DNI,