week-grid, week-header: properly initialize datetimes

Since we use autoptr on those, we may end up falling in to
the early return and mistakenly unreferencing the not
initialized new date.

src/views/gcal-week-grid.c

@@ -989,7 +989,9 @@ gcal_week_grid_drag_drop (GtkWidget      *widget,
   drop_cell = get_dnd_cell (widget, x, y);
   event_widget = gtk_drag_get_source_widget (context);
 
-  week_start = dnd_date = NULL;
+  week_start = NULL;
+  dnd_date = NULL;
+  new_end = NULL;
 
   if (!GCAL_IS_EVENT_WIDGET (event_widget))
     return FALSE;

src/views/gcal-week-header.c

@@ -1369,7 +1369,9 @@ gcal_week_header_drag_drop (GtkWidget      *widget,
   drop_cell = get_dnd_cell (widget, x, y);
   event_widget = gtk_drag_get_source_widget (context);
 
-  week_start = dnd_date = NULL;
+  week_start = NULL;
+  dnd_date = NULL;
+  new_end = NULL;
 
   if (!GCAL_IS_EVENT_WIDGET (event_widget))
     return FALSE;