From 0b721e0f37fc69ab197ec956a923e036e3b05ca6 Mon Sep 17 00:00:00 2001
From: Marcel Greter <marcel.greter@ocbnet.ch>
Date: Sun, 3 Nov 2019 01:06:18 +0100
Subject: [PATCH] Fix out of boundary vector access

Fixes https://github.com/sass/libsass/issues/2999
---
 src/ast_sel_weave.cpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/ast_sel_weave.cpp b/src/ast_sel_weave.cpp
index 2785ea370..c792d0f8a 100644
--- a/src/ast_sel_weave.cpp
+++ b/src/ast_sel_weave.cpp
@@ -576,8 +576,12 @@ namespace Sass {
       // Prepare data structures
       choices.push_back(expanded);
       choices.push_back({ group });
-      groups1.erase(groups1.begin());
-      groups2.erase(groups2.begin());
+      if (!groups1.empty()) {
+        groups1.erase(groups1.begin());
+      }
+      if (!groups2.empty()) {
+        groups2.erase(groups2.begin());
+      }
 
     }