fix(update_xnt): unset exitbypass after command_stop.sh in fn_update_localbuild

When the Xonotic server is not running during check-update, fn_update_localbuild
starts it temporarily to read the version from the console log, then stops it.
exitbypass=1 is set before command_stop.sh to prevent core_exit.sh from running
mid-flow, but command_stop.sh does not unset exitbypass when skipping core_exit.sh.
This caused the leaked exitbypass to bypass core_exit.sh at the end of
command_check_update.sh, returning control to core_getopt.sh which then printed
"Command did not exit correctly" and exited with code 2.

Fix: unset exitbypass explicitly after command_stop.sh returns.

Author: dgibbs64

lgsm/modules/update_xnt.sh

@@ -29,7 +29,9 @@ fn_update_localbuild() {
 		exitbypass=1
 		fn_sleep_time_5
 		tmux -L "${socketname}" send-keys -t "${sessionname}" "version" C-m > /dev/null 2>&1
+		exitbypass=1
 		command_stop.sh
+		unset exitbypass
 		fn_firstcommand_reset
 	fi