dir: free allocations on parse-error paths in `read_one_dir()`

dir: free allocations on parse-error paths in `read_one_dir()`

Two of `read_one_dir()`'s parse-error early returns leak ud.untracked
and ud.dirs. Plug them.

The other early returns in the same function are fine: they occur after
the `xmalloc()`+`memcpy()` that copies ud into `*untracked_`, at which
point ownership is transferred to the caller.
`read_untracked_extension()` then releases everything via
`free_untracked_cache()` on failure.

Pointed out by Coverity.

Assisted-by: Claude Opus 4.6
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>