Do not fail when there is no vndk namespace

Some of the legacy devices may not have vndk namespace. To make this
work, libnativeloader should not fail when it fails to search for vndk
namespace.

Bug: 129011845
Test: m -j
Change-Id: I6f68aeb6ae84a00985cc20561b2fcdb461be9724
Merged-In: Id9147d4aeee9ba2b301b6893dea5884dce9c14fa