Fix static analysis failures

src/freedombone-controlpanel

 
 function create_keydrive_fragment {
     select_user
-    if [ ! $SELECTED_USERNAME ]; then
+    if [ ! "$SELECTED_USERNAME" ]; then
         return
     fi
     dialog --title $"USB Fragment Keydrive" \
 
 function remove_backups {
     detect_usb_drive
+    # shellcheck disable=SC2154
     dialog --title $"Remove backups from a USB drive $USB_DRIVE" \
            --backtitle $"Freedombone Control Panel" \
            --defaultno \