From 0e5bcdef7fb592f986ad5b4e07b80d2efb5e3344 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Tue, 23 Oct 2018 00:39:44 -0700
Subject: [PATCH] [morx] Clear stack upon underflow when acting ligatures

---
 src/hb-aat-layout-morx-table.hh | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/hb-aat-layout-morx-table.hh b/src/hb-aat-layout-morx-table.hh
index ddb444c21..3f5f29d1d 100644
--- a/src/hb-aat-layout-morx-table.hh
+++ b/src/hb-aat-layout-morx-table.hh
@@ -402,7 +402,11 @@ struct LigatureSubtable
         do
 	{
 	  if (unlikely (!cursor))
+	  {
+	    /* Stack underflow.  Clear the stack. */
+	    match_length = 0;
 	    break;
+	  }
 
 	  buffer->move_to (match_positions[--cursor]);