Fix potential infinite loop in S_PaintChannels

when playing sounds with loop start >= end
(e.g. misc/forcefield.wav from Madfox's kaptlog.zip)

Quake/snd_mem.c

@@ -345,6 +345,12 @@ wavinfo_t GetWavinfo (const char *name, byte *wav, int wavlength)
 	else
 		info.samples = samples;
 
+	if (info.loopstart >= info.samples)
+	{
+		Con_Warning ("%s has loop start >= end\n", name);
+		info.loopstart = -1;
+	}
+
 	info.dataofs = data_p - wav;
 
 	return info;