week-header: don't attempt to add events incorrectly

One of the biggest issues of GNOME Calendar views right now
is that they rely on GObject property system to update the
active date. Even gcal_view_set_date() is just a wrapper
around GObject set.

Because GObject asynchronously updates the property by letting
the mainloop handle it, we can never be assured that all the
views had their views updated before updating the data model.

This patch temporarily adds sanity checks to GcalWeekHeader
to prevent making Calendar unusable, until we fix GcalView.

src/views/gcal-week-header.c

@@ -367,9 +367,10 @@ update_overflow (GcalWeekHeader *self)
           gtk_label_set_label (GTK_LABEL (label), text);
           g_free (text);
         }
-      else
+      else if (label)
         {
-          g_clear_pointer (&self->overflow_label[i], gtk_widget_destroy);
+          gtk_widget_destroy (label);
+          self->overflow_label[i] = NULL;
         }
     }
 
@@ -1668,6 +1669,13 @@ gcal_week_header_add_event (GcalWeekHeader *self,
   else
     end = 6;
 
+  /* Sanity checks */
+  if (start > end || start > 6 || end < 0)
+    {
+      g_warning ("Error adding event '%s' to the week header", gcal_event_get_summary (event));
+      return;
+    }
+
   /* Add the event widget to the grid */
   add_event_to_grid (self, event, start, end);