attr.c: make bootstrap_attr_stack() leave early
attr.c: make bootstrap_attr_stack() leave early

Thas would de-dent the body of a function that has grown rather large over
time, making it a bit easier to read.

Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

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