https://github.com/strukturag/libde265/commit/3e822a3ccf88df1380b165d6ce5a00494a27ceeb
Straight from upstream
To be removed with libde265-1.0.15 or later

From 3e822a3ccf88df1380b165d6ce5a00494a27ceeb Mon Sep 17 00:00:00 2001
From: Dirk Farin <dirk.farin@gmail.com>
Date: Thu, 23 Nov 2023 19:11:34 +0100
Subject: [PATCH] fix #432 (undefined IPM)

---
 libde265/image.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/libde265/image.h b/libde265/image.h
index 0b536054..0a0c0e32 100644
--- a/libde265/image.h
+++ b/libde265/image.h
@@ -624,7 +624,14 @@ struct de265_image {
 
   enum IntraPredMode get_IntraPredMode(int x,int y) const
   {
-    return (enum IntraPredMode)intraPredMode.get(x,y);
+    uint8_t ipm = intraPredMode.get(x,y);
+
+    // sanitize values if IPM is uninitialized (because of earlier read error)
+    if (ipm > 34) {
+      ipm = 0;
+    }
+
+    return static_cast<enum IntraPredMode>(ipm);
   }
 
   enum IntraPredMode get_IntraPredMode_atIndex(int idx) const