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>

builtin/rebase.c

@@ -253,6 +253,8 @@ static int apply_autostash(struct rebase_options *opts)
 
 	if (read_one(path, &autostash))
 		return error(_("Could not read '%s'"), path);
+	/* Ensure that the hash is not mistake for a number */
+	strbuf_addstr(&autostash, "^0");
 	argv_array_pushl(&stash_apply.args,
 			 "stash", "apply", autostash.buf, NULL);
 	stash_apply.git_cmd = 1;