Fix RC Pro Am II intro music and pulse phase reset behavior (#241)

References:
- RC Pro Am II, intro music square channels are wrong.
- apu_phase_reset.nes -
http://forums.nesdev.com/viewtopic.php?f=2&t=15346

src/sound.c

@@ -386,7 +386,8 @@ static void FASTAPASS(1) FrameSoundStuff(int V) {
 						mod = curfreq[P] >> (PSG[(P << 2) + 0x1] & 7);
 						if ((mod + curfreq[P]) & 0x800) {
 							sweepon[P] = 0;
-							curfreq[P] = 0;
+							/* https://github.com/TASVideos/fceux/issues/11 */
+							/* curfreq[P] = 0; */
 						} else {
 							if (curfreq[P] && (PSG[(P << 2) + 0x1] & 7)	/* && sweepon[P]&0x80*/) {
 								curfreq[P] += mod;
@@ -536,12 +537,13 @@ static INLINE void RDoSQ(int x) {
 	int32 cf;
 	int32 rc;
 
-	if (curfreq[x] < 8 || curfreq[x] > 0x7ff)
+	/* This has been updated in a section further down: */
+	/* if (curfreq[x] < 8 || curfreq[x] > 0x7ff)
 		goto endit;
 	if (!CheckFreq(curfreq[x], PSG[(x << 2) | 0x1]))
 		goto endit;
 	if (!lengthcount[x])
-		goto endit;
+		goto endit; */
 
 	if (EnvUnits[x].Mode & 0x1)
 		amp = EnvUnits[x].Speed;
@@ -568,6 +570,20 @@ static INLINE void RDoSQ(int x) {
 	cf = (curfreq[x] + 1) * 2;
 	rc = wlcount[x];
 
+	/* Testrom: apu_phase_reset.nes
+	 * http://forums.nesdev.com/viewtopic.php?f=2&t=15346 */
+	if (curfreq[x] < 8 || !CheckFreq(curfreq[x], PSG[(x << 2) | 0x1])
+	|| !lengthcount[x]) {
+		rc -= V;
+		if (rc <= 0) {
+			rc = cf - (-rc % cf);
+		}
+		V = 0;
+	}
+
+	if (rthresh == 6)	/* Reversed below */
+		currdc = (currdc - 2) & 0x7;
+
 	while (V > 0) {
 		if (currdc < rthresh)
 			*D += amp;
@@ -580,6 +596,9 @@ static INLINE void RDoSQ(int x) {
 		D++;
 	}
 
+	if (rthresh == 6)	/* Reverse above */
+		currdc = (currdc + 2) & 0x7;
+
 	RectDutyCount[x] = currdc;
 	wlcount[x] = rc;