Creating a custom QTextCodec when ICU is not used will cause it to not create the standard codecs when needed

Creating a custom QTextCodec when ICU is not used will cause it to not create the standard codecs when needed. The reason is because when it goes to initialize the standard codecs it checks if the list of codecs is not empty which it is not due to the fact that the custom one is already added to it. If ICU is enabled then this is not a problem as it still ensures that is available anyway.