packed_object_info_detail(): check for corrupt packfile.
packed_object_info_detail(): check for corrupt packfile.

Serge E. Hallyn noticed that we compute how many input bytes are
still left, but did not use it for sanity checking.

Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git