Allow GMSTs with empty EDID

apps/esmtool/tes4.cpp

@@ -97,6 +97,11 @@ namespace EsmTool
             return stream << " ?";
         }
 
+        std::ostream& operator<<(std::ostream& stream, const std::monostate&)
+        {
+            return stream << "[none]";
+        }
+
         std::ostream& operator<<(std::ostream& stream, const WriteData<ESM4::GameSetting::Data>& write)
         {
             std::visit([&](const auto& v) { stream << v; }, write.mValue);

components/esm4/loadgmst.cpp

@@ -13,7 +13,10 @@ namespace ESM4
         GameSetting::Data readData(FormId formId, std::string_view editorId, Reader& reader)
         {
             if (editorId.empty())
-                throw std::runtime_error("Unknown ESM4 GMST (" + formId.toString() + ") data type: editor id is empty");
+            {
+                reader.skipSubRecordData();
+                return std::monostate{};
+            }
             const char type = editorId[0];
             switch (type)
             {

components/esm4/loadgmst.hpp

@@ -13,7 +13,7 @@ namespace ESM4
 
     struct GameSetting
     {
-        using Data = std::variant<bool, float, std::int32_t, std::string>;
+        using Data = std::variant<std::monostate, bool, float, std::int32_t, std::string>;
 
         FormId mFormId; // from the header
         std::uint32_t mFlags; // from the header, see enum type RecordFlag for details