From b87ec263c780440f2e79ab29f3dea7a4bf02ba1d Mon Sep 17 00:00:00 2001
From: dgp <dgp@users.sourceforge.net>
Date: Fri, 6 May 2016 16:03:15 +0000
Subject: Bug fix. Have to arrange to only close a catch once.  After the space
 has been returned to placeholder values, closing with them as data leads to
 memory corruption.

There's probably a better fix available because the error here feels like
it's rooted somewhere else, having us continue to check values we ought to
know have already been closed.
---
 generic/tclAssembly.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/generic/tclAssembly.c b/generic/tclAssembly.c
index 6d5676b..d02721d 100644
--- a/generic/tclAssembly.c
+++ b/generic/tclAssembly.c
@@ -3984,6 +3984,9 @@ UnstackExpiredCatches(
 
     while (catchDepth > bbPtr->catchDepth) {
 	--catchDepth;
+	if (catches[catchDepth] == NULL) {
+	    continue;
+	}
 	range = envPtr->exceptArrayPtr + catchIndices[catchDepth];
 	range->numCodeBytes = bbPtr->startOffset - range->codeOffset;
 	catches[catchDepth] = NULL;
-- 
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