The fill_zeros parameter of WavegenFill is not used, so remove it.

src/libespeak-ng/speak_lib.c

 		out_ptr = outbuf;
 		out_end = &outbuf[outbuf_size];
 		event_list_ix = 0;
-		WavegenFill(0);
+		WavegenFill();
 
 		length = (out_ptr - outbuf)/2;
 		count_samples += length;

src/libespeak-ng/synthesize.h

 int  WavegenInitSound();
 void WavegenInit(int rate, int wavemult_fact);
 float polint(float xa[], float ya[], int n, float x);
-int WavegenFill(int fill_zeros);
+int WavegenFill();
 void MarkerEvent(int type, unsigned int char_position, int value, int value2, unsigned char *out_ptr);
 
 extern unsigned char *wavefile_data;

src/libespeak-ng/wavegen.c

 
 	event_list_ix = 0;
 
-	result = WavegenFill(1);
+	result = WavegenFill();
 
 	// copy from the outbut buffer into the portaudio buffer
 	if (result && (out_ptr > out_end2))
 	}
 }
 
-int WavegenFill2(int fill_zeros)
+int WavegenFill2()
 {
 	// Pick up next wavegen commands from the queue
 	// return: 0  output buffer has been filled
 				if (resume == 1)
 					return 0; // not yet finished
 			}
-
-			if (fill_zeros) {
-				while (out_ptr < out_end)
-					*out_ptr++ = 0;
-			}
 			return 1; // queue empty, close sound channel
 		}
 
 #endif
 
 // Call WavegenFill2, and then speed up the output samples.
-int WavegenFill(int fill_zeros)
+int WavegenFill()
 {
 	int finished;
 	unsigned char *p_start;
 
 	p_start = out_ptr;
 
-	// fill_zeros is ignored. It is now done in the portaudio callback
-	finished = WavegenFill2(0);
+	finished = WavegenFill2();
 
 #if HAVE_SONIC_H
 	if (sonicSpeed > 1.0) {

src/speak-ng.c

 	out_ptr = out_start = wav_outbuf;
 	out_end = wav_outbuf + sizeof(wav_outbuf);
 
-	finished = WavegenFill(0);
+	finished = WavegenFill();
 
 	if (quiet)
 		return finished;