Fix empty SUDO_USER variable bug

scripts/debian/postinst

@@ -6,11 +6,14 @@ case "$1" in
   configure)
     #echo "  Calling script"
     #/var/lib/dpkg/info/iri-comm-dev.hello_world
-    echo "  Addind user to dialout group..."
-    sudo usermod -a -G dialout $SUDO_USER
-    echo "  Done."
-    echo "  Adding 99-iri-comm-ftdi udev rule..."
 
+    if [ ! -z "$SUDO_USER" ]; then
+      echo "  Addind user to dialout group..."
+      sudo usermod -a -G dialout $SUDO_USER
+      echo "  Done."
+    fi
+
+    echo "  Adding 99-iri-comm-ftdi udev rule..."
     FILE="/lib/udev/rules.d/99-iri-comm-ftdi.rules"
     LINE0="#The following line allow the users on dialout to access SUBSYSTEM:VENDOR:PRODUCT=usb|usb_device:0403:6001 devices"
     LINE1="SUBSYSTEM==\"usb|usb_device\", ATTRS{idVendor}==\"0403\", ATTRS{idProduct}==\"6001\", GROUP=\"dialout\""