SDL_mixer: mixer: Fix crash when `MIX_PROP_PLAY_MAX_*` is less than start position. (d7305)

SDL Commits
1 
From d73052832eb61cf686b3455703e954a5eeb96dce Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <[EMAIL REDACTED]>
Date: Tue, 19 May 2026 10:18:37 -0400
Subject: [PATCH] mixer: Fix crash when `MIX_PROP_PLAY_MAX_*` is less than
 start position.

Total bytes read from the MIX_Track's audio stream would go negative, and then
many, many things would go wrong.

Fixes #855.

(cherry picked from commit 33fe7b125439c2a993580c22467d434c9fbc738c)
---
 src/SDL_mixer.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/SDL_mixer.c b/src/SDL_mixer.c
index 0deb5d74..e82a74dd 100644
--- a/src/SDL_mixer.c
+++ b/src/SDL_mixer.c
@@ -242,6 +242,8 @@ static void TrackStopped(MIX_Track *track)
 
 static void ApplyFade(MIX_Track *track, int channels, float *pcm, int frames)
 {
+    SDL_assert(frames >= 0);
+
     // !!! FIXME: this is probably pretty naive.
 
     if (track->fade_direction == 0) {
@@ -412,6 +414,9 @@ static void SDLCALL TrackGetCallback(void *userdata, SDL_AudioStream *stream, in
                 const Sint64 newpos = (Sint64)(track->position + frames_read);
                 if (newpos >= maxpos) {  // we read past the end of the fade out or maxframes, we need to clamp.
                     br -= (int)(((newpos - maxpos) * raw_channels) * sizeof(float));
+                    if (br < 0) {
+                        br = 0;
+                    }
                     frames_read = br / (sizeof (float) * raw_channels);
                     end_of_audio = true;
                 }