GameFile: Disallow mods from being converted

Source/Core/UICommon/GameFile.cpp

@@ -842,7 +842,8 @@ std::string GameFile::GetFileFormatName() const
 
 bool GameFile::ShouldAllowConversion() const
 {
-  return DiscIO::IsDisc(m_platform) && m_volume_size_type == DiscIO::DataSizeType::Accurate;
+  return DiscIO::IsDisc(m_platform) && m_volume_size_type == DiscIO::DataSizeType::Accurate &&
+         !IsModDescriptor();
 }
 
 bool GameFile::IsModDescriptor() const