The initial one was not doing enough to figure things out
without uncompressing too much.  It also fixes a potential
segfault resulting from missing use_packed_git() call.

We would need to introduce unuse_packed_git() call and do proper
use counting to figure out when it is safe to unmap, but
currently we do not unmap packed file yet.
Signed-off-by: NJunio C Hamano <junkio@cox.net>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>