[JFFS2] Handle dirents on the flash with embedded zero bytes in names.

In three places: summary scan, normal scan, REF_PRISTINE GC.

Just truncate at the NUL, since that was the correct thing to do in the
only case where this (inexplicable) breakage has been seen.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>

diff --cc fs/jffs2/gc.c
Simple merge

diff --cc fs/jffs2/scan.c
Simple merge

diff --cc fs/jffs2/summary.c
Simple merge