Audio playback fix

Do not apply the receive mixer volume to the audio
samples read from files when the mixer is disabled.

src/soundcard/sound.cxx

@@ -495,9 +495,11 @@ int cSoundOSS::Read(double *buffer, int buffersize)
 
 	if (playback) {
 		readPlayback( buffer, buffersize);
-		double vol = valRcvMixer->value();
-		for (int i = 0; i < buffersize; i++)
-			buffer[i] *= vol;
+		if (progdefaults.EnableMixer) {
+			double vol = valRcvMixer->value();
+			for (int i = 0; i < buffersize; i++)
+				buffer[i] *= vol;
+		}
 		return buffersize;
 	}
 
@@ -792,9 +794,11 @@ int cSoundPA::Read(double *buf, int count)
                 writeCapture(buf, count);
 	if (playback) {
 		readPlayback(buf, count);
-                double vol = valRcvMixer->value();
-                for (int i = 0; i < count; i++)
-                        buf[i] *= vol;
+		if (progdefaults.EnableMixer) {
+	                double vol = valRcvMixer->value();
+	                for (int i = 0; i < count; i++)
+        	                buf[i] *= vol;
+		}
 		return count;
 	}