event-editor/dialog: Don't show MOD_ALL if schedule changed

We get into seriously tricky situations if we try and change the
date & time of an event with recurrency, and pass MOD_ALL. That's
because it is ambioguous *where* the change must be applied.

Don't allow selecting MOD_ALL when the scheduling of the recurrent
event changes.

Fixes https://gitlab.gnome.org/GNOME/gnome-calendar/-/issues/882

src/gui/event-editor/gcal-event-editor-dialog.c

@@ -328,6 +328,7 @@ on_done_button_clicked_cb (GtkButton             *button,
   GcalCalendar *selected_calendar;
   GcalCalendar *calendar;
   GcalManager *manager;
+  gboolean schedule_changed;
   gint i;
 
   manager = gcal_context_get_manager (self->context);
@@ -336,6 +337,7 @@ on_done_button_clicked_cb (GtkButton             *button,
   if (gcal_calendar_is_read_only (calendar))
     GCAL_GOTO (out);
 
+  schedule_changed = FALSE;
   if (!self->event_is_new)
     {
       gboolean anything_changed = FALSE;
@@ -346,8 +348,16 @@ on_done_button_clicked_cb (GtkButton             *button,
 
           section_changed = gcal_event_editor_section_changed (self->sections[i]);
           anything_changed |= section_changed;
+
+          if (self->sections[i] == self->schedule_section)
+            schedule_changed = section_changed;
         }
 
+      GCAL_TRACE_MSG ("Event %s changed: %d, schedule changed: %d",
+                      gcal_event_get_uid (self->event),
+                      anything_changed,
+                      schedule_changed);
+
       if (!anything_changed)
         goto out;
     }
@@ -379,7 +389,7 @@ on_done_button_clicked_cb (GtkButton             *button,
     {
       gcal_utils_ask_recurrence_modification_type (GTK_WIDGET (self),
                                                    self->event,
-                                                   TRUE,
+                                                   !schedule_changed,
                                                    on_ask_recurrence_response_save_cb,
                                                    self);
       return;