Stream name decoding with chained name IV was broken because chained
name IV computation was unconditionally padding each path element
whereas that should only be done for block name I/O algorithm. Fix
uses each path element as is for chained IV computation with stream
name algorithm.
Also added an integration test case containing a volume created with
encfs 1.7.4 that uses stream name algorithm and chained name IV
with a directory and a test file in that directory to exercise the
path that fails without this commit.