Commit bbd37149e4 for ffmpeg

commit bbd37149e4b1bd9730a70f06b72d1c1f9b95bc0f
Author: Leo Izen <leo.izen@gmail.com>
Date:   Sat Oct 17 12:49:36 2026 -0400

    avcodec/pngdec: avoid implementation-defined right-shift behavior

    Right shifting a negative-signed integer has implementation-defined
    behavior with regard to sign-extending or zero-extending. Taking the
    result and a bitwise-and mask makes this work regardless of that
    behavior.

    Signed-off-by: Leo Izen <leo.izen@gmail.com>

diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index f20cef76d9..58c688e51f 100644
--- a/libavcodec/pngdec.c
+++ b/libavcodec/pngdec.c
@@ -520,7 +520,7 @@ static char *iso88591_to_utf8(const char *in, size_t size_in)
         return NULL;
     for (i = 0; i < size_in; i++) {
         if (in[i] & 0x80) {
-            *(q++) = 0xC0 | (in[i] >> 6);
+            *(q++) = 0xC0 | ((in[i] >> 6) & 0x3);
             *(q++) = 0x80 | (in[i] & 0x3F);
         } else {
             *(q++) = in[i];