audio: Patched to compile on Visual Studio.

(It gets upset at the -2147483648, thinking this should be an unsigned value
because 2147483648 is too large for an int32, so the negative sign upsets the
compiler.)

src/audio/SDL_audiotypecvt.c

@@ -279,7 +279,7 @@ SDL_Convert_F32_to_S32_Scalar(SDL_AudioCVT *cvt, SDL_AudioFormat format)
         if (sample >= 1.0f) {
             *dst = 2147483647;
         } else if (sample <= -1.0f) {
-            *dst = -2147483648;
+            *dst = (Sint32) -2147483648LL;
         } else {
             *dst = ((Sint32)(sample * 8388607.0f)) << 8;
         }