sndio: Fix for some platforms (Linux, for example) that don't define INFTIM.

Fixes Bugzilla #3712.

src/audio/sndio/SDL_sndioaudio.c

@@ -44,6 +44,10 @@
 #include "SDL_loadso.h"
 #endif
 
+#ifndef INFTIM
+#define INFTIM -1
+#endif
+
 static struct sio_hdl * (*SNDIO_sio_open)(const char *, unsigned int, int);
 static void (*SNDIO_sio_close)(struct sio_hdl *);
 static int (*SNDIO_sio_setpar)(struct sio_hdl *, struct sio_par *);