[NFC][Clang] Fix static analyzer concern about null value derefence

[tahonermann]

Looks fine to me!

clang/lib/Serialization/ASTReaderDecl.cpp

case UPD_CXX_ADDED_VAR_DEFINITION: {
       break;
     }
 
     case UPD_CXX_POINT_OF_INSTANTIATION: {
       SourceLocation POI = Record.readSourceLocation();
       if (auto *VTSD = dyn_cast<VarTemplateSpecializationDecl>(D)) {
         VTSD->setPointOfInstantiation(POI);
       } else if (auto *VD = dyn_cast<VarDecl>(D)) {
-        VD->getMemberSpecializationInfo()->setPointOfInstantiation(POI);
+        MemberSpecializationInfo *MSInfo = VD->getMemberSpecializationInfo();
+        assert(MSInfo && "No member specialization information");
+        MSInfo->setPointOfInstantiation(POI);
       } else {
         auto *FD = cast<FunctionDecl>(D);
         if (auto *FTSInfo = FD->TemplateOrSpecialization
                     .dyn_cast<FunctionTemplateSpecializationInfo *>())
           FTSInfo->setPointOfInstantiation(POI);
         else
           FD->TemplateOrSpecialization.get<MemberSpecializationInfo *>()
               ->setPointOfInstantiation(POI);