diff.c: fix "size cache" handling.
diff.c: fix "size cache" handling.

We broke the size-cache handling when we changed the function
signature of sha1_object_info() in 21666f1a.  We obviously
wanted to cache the size we obtained when sha1_object_info()
succeeded, not when it failed.

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