Vulkan handles are either pointers (64-bit) or 64-bit integer
handles (32-bit). Cast the type in failure cases.
vkwindow.c:229:561: error: return makes integer from pointer without a cast [-Werror=int-conversion]
vkwindow.c:231:194: error: return makes integer from pointer without a cast [-Werror=int-conversion]
https://bugzilla.gnome.org/show_bug.cgi?id=777979