From 2fea10ad03c22d3299c56a45370598501d7ee7cf Mon Sep 17 00:00:00 2001
From: Gregory Maxwell <greg@xiph.org>
Date: Sun, 2 Apr 2017 21:28:17 +0000
Subject: [PATCH] Make GetWitnessCommitmentIndex callable on blocks without a
 coinbase txn.

This isn't actually needed anywhere, but it's less brittle.

Github-Pull: #10146
Rebased-From: ada0caa165905b50db351a56ec124518c922085a
---
 src/validation.cpp | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/validation.cpp b/src/validation.cpp
index 5643d2ab5..43ef8c88f 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -2922,9 +2922,11 @@ bool IsWitnessEnabled(const CBlockIndex* pindexPrev, const Consensus::Params& pa
 static int GetWitnessCommitmentIndex(const CBlock& block)
 {
     int commitpos = -1;
-    for (size_t o = 0; o < block.vtx[0]->vout.size(); o++) {
-        if (block.vtx[0]->vout[o].scriptPubKey.size() >= 38 && block.vtx[0]->vout[o].scriptPubKey[0] == OP_RETURN && block.vtx[0]->vout[o].scriptPubKey[1] == 0x24 && block.vtx[0]->vout[o].scriptPubKey[2] == 0xaa && block.vtx[0]->vout[o].scriptPubKey[3] == 0x21 && block.vtx[0]->vout[o].scriptPubKey[4] == 0xa9 && block.vtx[0]->vout[o].scriptPubKey[5] == 0xed) {
-            commitpos = o;
+    if (!block.vtx.empty()) {
+        for (size_t o = 0; o < block.vtx[0]->vout.size(); o++) {
+            if (block.vtx[0]->vout[o].scriptPubKey.size() >= 38 && block.vtx[0]->vout[o].scriptPubKey[0] == OP_RETURN && block.vtx[0]->vout[o].scriptPubKey[1] == 0x24 && block.vtx[0]->vout[o].scriptPubKey[2] == 0xaa && block.vtx[0]->vout[o].scriptPubKey[3] == 0x21 && block.vtx[0]->vout[o].scriptPubKey[4] == 0xa9 && block.vtx[0]->vout[o].scriptPubKey[5] == 0xed) {
+                commitpos = o;
+            }
         }
     }
     return commitpos;