SDL_mixer: fluidsynth: fix more -Wsign-compare warnings missed in prev. commit.

SDL Commits
1 
From 74ffed9455522a75ecb87b528d8924268e2cdf2c Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Fri, 9 Jan 2026 02:23:02 +0300
Subject: [PATCH] fluidsynth: fix more -Wsign-compare warnings missed in prev.
 commit.

---
 src/decoder_fluidsynth.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/decoder_fluidsynth.c b/src/decoder_fluidsynth.c
index 39741373..1c296275 100644
--- a/src/decoder_fluidsynth.c
+++ b/src/decoder_fluidsynth.c
@@ -208,7 +208,15 @@ static void *SoundFontOpen(const char *filename)
 
 static int SoundFontRead(void *buf, fluid_long_long_t count, void *handle)
 {
-    return (SDL_ReadIO((SDL_IOStream *) handle, buf, count) == count) ? FLUID_OK : FLUID_FAILED;
+    #if (SDL_SIZE_MAX < SDL_MAX_SINT64)
+    if (count > (fluid_long_long_t)(SDL_MAX_UINT32)) {
+        return FLUID_FAILED;
+    }
+    #endif
+    if (count < 0) {
+        return FLUID_FAILED;
+    }
+    return (SDL_ReadIO((SDL_IOStream *) handle, buf, count) == (size_t)count) ? FLUID_OK : FLUID_FAILED;
 }
 
 static int SoundFontSeek(void *handle, fluid_long_long_t offset, int origin)