rebase (autostash): use an explicit OID to apply the stash

rebase (autostash): use an explicit OID to apply the stash

When `git stash apply <argument>` sees an argument that consists only of
digits, it tries to be smart and interpret it as `stash@{<number>}`.

Unfortunately, an all-digit hash (which is unlikely but still possible)
is therefore misinterpreted as `stash@{<n>}` reflog.

To prevent that from happening, let's append `^0` after the stash hash,
to make sure that it is interpreted as an OID rather than as a number.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Reviewed-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>