It is a little confusing, but you need to validate the first value (the full file name) not just the extension... so the code should be:
$WAFV_Errors .= WAValidateFE(((isset($_FILES["vendorLogo"]))?$_FILES["vendorLogo"]["name"]:"") . "",".gif, .jpg, .jpeg, .png",true,2);
When you choose just the extension, then it removes the "." in front, and that won't validate properly. The File Extension validation will automatically strip the file name and validate just the extension part.