wayland: Fix nulltpr dereference on deprecated swapchains
Fixes a nulltpr dereference when a buffer release event is processed on deprecated swapchains. In such a case some of the swapchain images are invalid and associated resources have been freed.
Change-Id: I8f1c66e42e900d63c8c43cb53068a8aee9ea25a9 Signed-off-by: Rosen Zhelev rosen.zhelev@arm.com