Jakub Jelinek points out that current fix has an underflow problem
if elf_ppnt->p_filesz == 0.  Fix that up, and also stop overwriting
interpreter buffer, simply check that it's NULL-terminated.

From: Jakub Jelinek <jakub@redhat.com>
Signed-off-by: Chris Wright <chrisw@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>