Handling missing captions button better

There was a bug introduced in 86a53b4
that caused a dependency between existence of the captionsButton and the
captionsMuted property. However, there are many cases where there is no
visible captions button but the developer would like to control captions
from another UI interaction/element/mechanism. This should fix that
functionality

Author: chipbell4

src/container/plugins/CaptionsPlugin.js

@@ -65,17 +65,15 @@
 		 */
 		this.captionsButton = document.querySelector(this.options.captionsButton);
 
-		if (null === this.captionsButton)
+		if (null !== this.captionsButton)
 		{
-			return;
-		}
-
-		this.captionsButtonClick = function()
-		{
-			this.captionsMuted = !this.captionsMuted;
-		}.bind(this);
+			this.captionsButtonClick = function()
+			{
+				this.captionsMuted = !this.captionsMuted;
+			}.bind(this);
 
-		this.captionsButton.addEventListener('click', this.captionsButtonClick);
+			this.captionsButton.addEventListener('click', this.captionsButtonClick);
+		}
 
 		/**
 		 * Set the captions are enabled or not
@@ -194,8 +192,11 @@
 		// Handle the features request
 		this.on('features', function(features)
 		{
-			this.captionsButton.style.display = 'none';
-			if (features.captions) this.captionsButton.style.display = 'inline-block';
+			if (null !== this.captionsButton)
+			{
+				this.captionsButton.style.display = 'none';
+				if (features.captions) this.captionsButton.style.display = 'inline-block';
+			}
 		});
 
 		//Set the defaults if we have none for the controls
@@ -207,35 +208,31 @@
 
 	plugin.opened = function()
 	{
-		if (null === this.captionsButton)
+		if (null !== this.captionsButton)
 		{
-			return;
+			this.captionsButton.classList.remove('disabled');
 		}
 
-		this.captionsButton.classList.remove('disabled');
 		this.captionsMuted = !!SavedData.read(CAPTIONS_MUTED);
 		this.setCaptionsStyles(SavedData.read(CAPTIONS_STYLES));
 	};
 
 	plugin.close = function()
 	{
-		if (null === this.captionsButton)
+		if (null !== this.captionsButton)
 		{
-			return;
+			this._disableButton(this.captionsButton);
 		}
-
-		this._disableButton(this.captionsButton);
 	};
 
 	plugin.teardown = function()
 	{
-		if (null === this.captionsButton)
+		if (null !== this.captionsButton)
 		{
-			return;
+			this.captionsButton.removeEventListener('click', this.captionsButtonClick);
+			delete this.captionsButton;
 		}
 
-		this.captionsButton.removeEventListener('click', this.captionsButtonClick);
-		delete this.captionsButton;
 		delete this._captionsStyles;
 		delete this.getCaptionsStyles;
 		delete this.setCaptionsStyles;