Unmounting usb drive

src/freedombone-utils-keys

             fi
         fi
 
-        backup_unmount_drive ${USB_DRIVE}
+        if [ -d $USB_MOUNT ]; then
+            backup_unmount_drive ${USB_DRIVE}
+        fi
         if [[ $GPG_LOADING == "yes" ]]; then
             dialog --title $"Recover Encryption Keys" \
                    --msgbox $"Now remove the USB drive. Insert the next drive containing a key fragment, or select Ok to finish" 6 70