From 5a4786169de5cc3cf4dc29a32f61033ff7b370d1 Mon Sep 17 00:00:00 2001
From: Philip Monk <phil@pcmonk.me>
Date: Tue, 31 Mar 2020 11:33:10 -0700
Subject: [PATCH] clay: don't underflow when patch produces empty file

Fixes #2602

I haven't been able to reproduce this bug, but I can see how it could
happen in theory.  This should resolve the issue.
---
 bin/solid.pill              | 4 ++--
 pkg/arvo/sys/vane/clay.hoon | 2 ++
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/bin/solid.pill b/bin/solid.pill
index ed6ae9d58..e03e2edf5 100644
--- a/bin/solid.pill
+++ b/bin/solid.pill
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:0b317cdb5fccee9afbebd16a3f5ff14a0138af893e9ca03da4af6effb34ea2bd
-size 13101105
+oid sha256:c9609b017c0fb9e4797e6a5f6e1052ae70725b4178f8ba18e7cef3c6ed1489c5
+size 13109549
diff --git a/pkg/arvo/sys/vane/clay.hoon b/pkg/arvo/sys/vane/clay.hoon
index c53ea09c3..d4c08fd22 100644
--- a/pkg/arvo/sys/vane/clay.hoon
+++ b/pkg/arvo/sys/vane/clay.hoon
@@ -2563,6 +2563,8 @@
       =+  dif=;;((urge cord) q.r.bol)
       =,  format
       =+  pac=(of-wain (lurk:differ (to-wain (cat 3 txt '\0a')) dif))
+      ?~  pac
+        ''
       (end 3 (dec (met 3 pac)) pac)
     ::
     ::  Traverse an ankh.