[Antergos and Manjaro support] [Download latest detect_linux.sh if bundled script returns unknown] [Display error message if OS is detected as unknown]

src/helpers.js

@@ -140,7 +140,9 @@ module.exports.downloadFile = (url, destination, progressCallback, completeCallb
       response.data.on('data', (chunk) => {
         stream.write(Buffer.from(chunk));
         downloaded += chunk.length;
-        progressCallback((downloaded / total * 100.0).toFixed(2));
+        if (progressCallback) {
+          progressCallback((downloaded / total * 100.0).toFixed(2));
+        }
       });
 
       response.data.on('end', () => {