Looks like the XRestartManager keeps all command line arguments when
restarting, so it also keeps --safe-mode.

Solution is to add a flag file when restarting from safe mode,
to prevent going into safe mode again.

Change-Id: I9820d3ccbddf98b0bf6132f254c989f52ea5e808
Reviewed-on: https://gerrit.libreoffice.org/31913Reviewed-by: Samuel Mehrbrodt <Samuel.Mehrbrodt@cib.de>
Tested-by: Samuel Mehrbrodt <Samuel.Mehrbrodt@cib.de>