fixed bug where scrolling right (at certain screen widths) fails

See the following HTML for an example
```
<!DOCTYPE html>
<html lang="en" xmlns="http://www.w3.org/1999/xhtml">
<head>
    <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
    <script src='https://rawgithub.com/9bitStudios/flexisel/master/js/jquery.flexisel.js'></script>
    <meta charset="utf-8" />
    <title>Flexisel bug demonstration</title>
    <style>
		.video-gallery-wrapper .video-thumbs .video-thumb img {
			max-width: 100%;
			height: auto;
		}
		.video-gallery-wrapper .video-thumbs .video-thumb:nth-child(3n+3) {
			margin-right: 0; 
		}
		.video-gallery-wrapper .video-thumbs .video-thumb:first-child {
			padding-left: 0; 
		}
		.video-gallery-wrapper .video-thumbs .video-thumb .video-caption {
			display: block;
			padding: 10px 10px 10px 10px;
			font-size: 10pt;
			float: left;
			color: #2070b6; 
		}
		.video-gallery-wrapper .video-thumbs .video-thumb > a:after {
			clear: both;
			display: block;
			content: ""; 
		}
		.video-gallery-wrapper .nbs-flexisel-inner {
			margin-bottom: 15px; 
		}
		@media only screen and (min-width: 580px) {
			.video-thumbs .video-thumb {
				max-width: 23.5%; 
			}
			.video-thumbs .video-thumb:nth-child(4n+4) {
				margin-right: 0; 
			} 
		}
		.video-gallery-title {
			padding: 5px 5px 5px 8px;
			font-size: 14pt; 
		}
		.nbs-flexisel-container {
			position: relative;
			max-width: 100%; 
		}
		.nbs-flexisel-ul {
			position: relative;
			width: 9999px;
			margin: 0px;
			padding: 0px;
			list-style-type: none;
			text-align: left; 
		}
		.nbs-flexisel-inner {
			overflow: hidden;
			float: left;
			width: 100%;
			background: #eeeeee;
			border-top: none; 
		}
		.nbs-flexisel-item {
			float: left;
			margin: 0px;
			padding: 0px;
			cursor: pointer;
			position: relative;
			line-height: 0px; 
		}
		.nbs-flexisel-item img {
			max-width: 32%;
			padding: 1px;
			float: left; 
		}
		/*** Navigation ***/
		.nbs-flexisel-nav-left,
		.nbs-flexisel-nav-right {
			height: 40px;
			width: 40px;
			background: #fff;
			position: absolute;
			cursor: pointer;
			z-index: 1000; 
		}
		.nbs-flexisel-nav-left {
			left: 0;
		}
		.nbs-flexisel-nav-left:after {
			content: "<"; 
		}
		.nbs-flexisel-nav-right {
			right: 0; 
		}
		.nbs-flexisel-nav-right:after {
			content: ">"; 
		}
    </style>
</head>
<body>
	<p>
		At certain screen widths you can't scroll to the next image:<br/>
		Screen Width - 808px:broken<br />
		Screen Width - 809px:works<br />
		Screen Width - 810px:works<br />
		Screen Width - 811px:works<br />
		Screen Width - 812px:broken
	</p>
	<div class="video-gallery-wrapper">
		<ul class="video-thumbs"></ul>
	</div>
</body>
<script type="text/javascript">
	for (var i=0; i<5; i++) {
		$(".video-thumbs").append('<li class="video-thumb"><a class="video" href="javascript:void(0)"><img class="video-thumbnail-image" src="http://freetopwallpaper.com/wp-content/gallery/cat/cute-cats-wallpapers-background-35.jpg" alt="Test"/><span class="video-caption">blah blah blah</span></a></li>');
	}
	$(".video-thumbs").flexisel({
		enableResponsiveBreakpoints: true,
		clone: false,
		responsiveBreakpoints: {
			mobile: {
				changePoint: 579,
				visibleItems: 2
			},
			tablet: {
				changePoint: 580,
				visibleItems: 3
			},
			desktop: {
				changePoint: 900,
				visibleItems: 4
			}
		}
	});
</script>
</html>
```