[PATCH 1 of 2] dirstate: fix parse_dirstate() to error out if NULL entry created

[Yuya Nishihara]

# HG changeset patch
# User Yuya Nishihara <yuya at tcha.org>
# Date 1632383057 -32400
#      Thu Sep 23 16:44:17 2021 +0900
# Node ID 13efd8fdc55fe3ed8ab195fff0c52a249d4dcc73
# Parent  1b2ee68e85f93c0726db9f2f739bc6768db1f92f
dirstate: fix parse_dirstate() to error out if NULL entry created

Since 83f0e93ec34b "dirstate-item: move the C implementation to the same
logic", dirstate_item_from_v1_data() gets more likely to return NULL, and
the fuzzer crashes because of that.

diff --git a/mercurial/cext/parsers.c b/mercurial/cext/parsers.c
--- a/mercurial/cext/parsers.c
+++ b/mercurial/cext/parsers.c
@@ -770,6 +770,8 @@ static PyObject *parse_dirstate(PyObject
 
 		entry = (PyObject *)dirstate_item_from_v1_data(state, mode,
 		                                               size, mtime);
+		if (!entry)
+			goto quit;
 		cpos = memchr(cur, 0, flen);
 		if (cpos) {
 			fname = PyBytes_FromStringAndSize(cur, cpos - cur);