Fix explicit specialization in non-namespace scope

Although MSVC compiles specializations inside non-specialized classes,
this is against C++17 17.8.3/17. Instead we use C++17's "if constexpr".

Author: Zegeri

src/xrGame/ini_id_loader.h

@@ -32,39 +32,24 @@ class CIni_IdToIndex
     static T_VECTOR* m_pItemDataVector;
 
     template <u32 NUM>
-    static void LoadItemData(u32, LPCSTR)
-    {
-        static_assert(std::is_same_v<decltype(NUM), bool>, "Specialization for LoadItemData in CIni_IdToIndex not found."); // Xottab_DUTY: Is this correct?
-        NODEFAULT;
-    }
-
-    template <>
-    static void LoadItemData<0>(u32 count, LPCSTR cfgRecord)
+    static void LoadItemData(u32 count, LPCSTR cfgRecord)
     {
+        static_assert(NUM < 2, "Specialization for LoadItemData in CIni_IdToIndex not found."); // Xottab_DUTY: Is this correct?
         for (u32 k = 0; k < count; k += 1)
         {
             string64 buf;
             LPCSTR id_str = _GetItem(cfgRecord, k, buf);
-            char* id_str_lwr = xr_strdup(id_str);
-            xr_strlwr(id_str_lwr);
-            ITEM_DATA item_data(T_INDEX(m_pItemDataVector->size()), T_ID(id_str));
-            m_pItemDataVector->push_back(item_data);
-            xr_free(id_str_lwr);
-        }
-    }
-
-    template <>
-    static void LoadItemData<1>(u32 count, LPCSTR cfgRecord)
-    {
-        for (u32 k = 0; k < count; k += 2)
-        {
-            string64 buf, buf1;
-            LPCSTR id_str = _GetItem(cfgRecord, k, buf);
-            char* id_str_lwr = xr_strdup(id_str);
+            char* id_str_lwr = xr_strdup(id_str); // not used
             xr_strlwr(id_str_lwr);
-            LPCSTR rec1 = _GetItem(cfgRecord, k + 1, buf1);
-            ITEM_DATA item_data(T_INDEX(m_pItemDataVector->size()), T_ID(id_str), rec1);
-            m_pItemDataVector->push_back(item_data);
+            if constexpr (NUM == 0) {
+                ITEM_DATA item_data(T_INDEX(m_pItemDataVector->size()), T_ID(id_str));
+                m_pItemDataVector->push_back(item_data);
+            } else {
+                string64 buf1;
+                LPCSTR rec1 = _GetItem(cfgRecord, k + 1, buf1);
+                ITEM_DATA item_data(T_INDEX(m_pItemDataVector->size()), T_ID(id_str), rec1);
+                m_pItemDataVector->push_back(item_data);
+            }
             xr_free(id_str_lwr);
         }
     }