HDFS-16923. [SBN read] getlisting RPC to observer will throw NPE if path does not exist (#5400)

Signed-off-by: Erik Krogen <xkrogen@apache.org>

(cherry picked from commit 6bd24448154fcd3ab9099d7783cc7f7f76c61e08)
(cherry picked from commit a7c1fad0c9a675195579c971962ddd32e5d9fc51)
2 files changed