[PATCH 2 of 4 V2] sparse-revlog: handle nullrev in index_get_start

[Boris Feld]

# HG changeset patch
# User Boris Feld <boris.feld at octobus.net>
# Date 1544804621 -3600
#      Fri Dec 14 17:23:41 2018 +0100
# Node ID 216e6d5c773cd51c18e351b11a8105165d2ad2d7
# Parent  c1e47daaab82e7d9340b0bd179d022fdd21062fc
# EXP-Topic sparse-followup
# Available At https://bitbucket.org/octobus/mercurial-devel/
#              hg pull https://bitbucket.org/octobus/mercurial-devel/ -r 216e6d5c773c
sparse-revlog: handle nullrev in index_get_start

The more generic index_get method handle nullrev fine, we apply the same logic
here.

diff --git a/mercurial/cext/revlog.c b/mercurial/cext/revlog.c
--- a/mercurial/cext/revlog.c
+++ b/mercurial/cext/revlog.c
@@ -190,6 +190,9 @@ static inline int index_get_parents(inde
 
 static inline int64_t index_get_start(indexObject *self, Py_ssize_t rev)
 {
+	if (rev == nullrev) {
+		return 0;
+	}
 	uint64_t offset;
 	if (rev >= self->length) {
 		PyObject *tuple;