Mark divelist as changed if user accepts planned dive

When the user clicks OK in the dive planner and the dive is added to the
divelist the divelist needs to be marked as changed so Subsurface prompts
the user to save the file before quitting.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

planner.c

@@ -618,6 +618,7 @@ void plan(struct diveplan *diveplan, char **cached_datap, struct dive **divep)
 	add_plan_to_notes(diveplan, dive);
 	/* now make the dive visible in the dive list */
 	report_dives(FALSE, FALSE);
+	mark_divelist_changed(TRUE);
 	show_and_select_dive(dive);
 	free(stoplevels);
 	free(gaschanges);