I haven't done the RCS id on the patchfile which looks like it's common in pkgsrc, that'll change the checksum as well.
diff -r 6efb1b750b38 net/librsync/Makefile
--- a/net/librsync/Makefile Fri Sep 16 09:42:25 2016 +0000
+++ b/net/librsync/Makefile Mon Sep 19 13:12:00 2016 -0700
@@ -1,6 +1,7 @@
# $NetBSD: Makefile,v 1.3 2016/09/01 16:16:55 wiz Exp $
DISTNAME= librsync-2.0.0
+PKGREVISION= 1
CATEGORIES= net
MASTER_SITES= ${MASTER_SITE_GITHUB:=librsync/}
GITHUB_TAG= v${PKGVERSION_NOREV}
diff -r 6efb1b750b38 net/librsync/distinfo
--- a/net/librsync/distinfo Fri Sep 16 09:42:25 2016 +0000
+++ b/net/librsync/distinfo Mon Sep 19 13:12:00 2016 -0700
@@ -4,3 +4,4 @@
RMD160 (librsync-2.0.0.tar.gz) = f44284c0d33b9fb6a9b8c107169549cf2d121273
SHA512 (librsync-2.0.0.tar.gz) = 1a88dcc3aa60949e058c57eb0df3e0086823c493de40fed927246f5aada6274db57202074456a0ce5d9aa8b81b41836b0d6221ded6a75d43829572584177e8c0
Size (librsync-2.0.0.tar.gz) = 155049 bytes
+SHA1 (patch-search.c) = 4c64cdf5740b72f37f8f0a3664338365e14668b4
diff -r 6efb1b750b38 net/librsync/patches/patch-search.c
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/net/librsync/patches/patch-search.c Mon Sep 19 13:12:00 2016 -0700
@@ -0,0 +1,11 @@
+--- src/search.c.orig 2016-09-16 14:04:07.000000000 -0700
++++ src/search.c 2016-09-16 14:05:01.000000000 -0700
+@@ -218,7 +218,7 @@
+ r = m;
+ }
+
+- if (l == r) {
++ if ((l == r) && (l <= bucket->r)) {
+ int i = sig->targets[l].i;
+ rs_block_sig_t *b = &(sig->block_sigs[i]);
+ if (weak_sum != b->weak_sum)