Fix #6460: Crash when reading corrupt object files

- Move sawyer coding functions to SawyerChunkReader.
- Replace assertions with exceptions to prevent crash on invalid chunks.

src/openrct2/object/ObjectRepository.cpp

@@ -363,7 +363,7 @@ private:
         std::sort(_items.begin(), _items.end(), [](const ObjectRepositoryItem &a,
                                                    const ObjectRepositoryItem &b) -> bool
         {
-            return strcmp(a.Name, b.Name) < 0;
+            return String::Compare(a.Name, b.Name) < 0;
         });
 
         // Fix the IDs