Fix bugs causing the disc spinning noise to never stop. (#285)

- Hard reset would lose track of state.
- The 1770 driver would often cause bad state upon an error.

6502.js

@@ -936,6 +936,7 @@ define(['./utils', './6502.opcodes', './via', './acia', './serial', './tube', '.
                     this.touchScreen = new TouchScreen(this.scheduler);
                     this.acia = new Acia(this, this.soundChip.toneGenerator, this.scheduler, this.touchScreen);
                     this.serial = new Serial(this.acia);
+                    this.ddNoise.spinDown();
                     this.fdc = new model.Fdc(this, this.ddNoise, this.scheduler);
                     this.crtc = this.video.crtc;
                     this.ula = this.video.ula;

ddnoise.js

@@ -88,6 +88,11 @@ define(['./utils', 'underscore', 'promise'], function (utils, _) {
         this.state = SPIN_UP;
         var self = this;
         this.play(this.sounds.motorOn).then(function () {
+            // Handle race: we may have had spinDown() called on us before the
+            // spinUp() initial sound finished playing.
+            if (self.state === IDLE) {
+                return;
+            }
             self.play(self.sounds.motor, true).then(function (source) {
                 self.motor = source;
                 self.state = SPINNING;