pathspec: use match for sparse-index expansion checks

The pathspec parser computes `len` and `nowildcard_len` from `item.match`, which includes any prefix added when a command is run from a subdirectory. `item.original` can still contain the shorter, unprefixed argument. Using `item.original + item.nowildcard_len` in `pathspec_needs_expanded_index()` can therefore read past the end of the allocation. AddressSanitizer reports a heap-buffer-overflow for prefixed wildcard pathspecs passed to `git rm` and `git reset` with a sparse index. The mismatch dates back to 4d1cfc1351 ("reset: make --mixed sparse-aware", 2021-11-29), which introduced the helper using `item.original`. b29ad38322 ("pathspec.h: move pathspec_needs_expanded_index() from reset.c to here", 2022-08-07) later moved it to `pathspec.c` and preserved the affected comparisons. Use `item.match` consistently when checking whether a pathspec can match a sparse-directory entry. Add coverage for prefixed wildcard pathspecs so both commands keep the index sparse. Signed-off-by: Ted Nyman <tnyman@openai.com> Reviewed-by: Taylor Blau <ttaylorr@openai.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>