Revert "wavegen.c: Fix -Wunused-but-set-variable warning."

This reverts commit 6d751c93bf.

Fixes https://github.com/nvaccess/nvda/issues/8231.

src/libespeak-ng/wavegen.c

@@ -1397,14 +1397,13 @@ static int SpeedUp(short *outbuf, int length_in, int length_out, int end_of_text
 int WavegenFill(void)
 {
 	int finished;
-
-	finished = WavegenFill2();
-
-#if HAVE_SONIC_H
 	unsigned char *p_start;
 
 	p_start = out_ptr;
 
+	finished = WavegenFill2();
+
+#if HAVE_SONIC_H
 	if (sonicSpeed > 1.0) {
 		int length;
 		int max_length;