chimera: fix NPE on '.(parent)()' for root inode

Acked-by: Albert Rossi
Acked-by: Dmitry Litvintsev
Target: master, 2.10, 2.9, 2.8, 2.7, 2.6
Require-book: no
Require-notes: no
(cherry picked from commit 82879878110e5254ae1314c759a5fc4f26aecf0c)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Merge pull request #849 from kofemann/fix-chimera-npe-2.6

chimera: fix NPE on '.(parent)()' for root inode