Resource map -> SCI Version detection

Johannes Good day
I dont know if the is the correct forum to ask but here goes. I want to know what the criteria is for validating that a file is in the SCI0 version of the SCI file format. As I have looked at the SCI Studio code and it confuses me in LoadResourceMap procedure on Line : 1428 in the rexplorer.cpp file. Where the if statement that looks as follows :
//====== START SNIP ========/
&&ResourceMapData[20]) {
//====== END SNIP ========/

Occording to this the default file must not be a valid file as the 0 and 3 entry of the file is 0, thus resulting in a FALSE. Can somebody please give me some clarity on this please.

Thanks in Advance

Johannes Pretorius