Improve charting UI for error cases

Web/Views/Chart/Index.cshtml

@@ -1,13 +1,17 @@
 @model LeafWeb.Web.ViewModels.Chart.ChartViewModel
 @{
     ViewBag.Title = "Chart";
+    var selectText = "Select CurveId";
 }
 <h1>@ViewBag.Title</h1>
 <h3>Identifier: <strong>@Model.LeafInputIdentifier</strong></h3>
 
-@Html.DropDownList("CurveId", new SelectList(Model.AvailableCurveId, Model.CurveId), "Select CurveId")
+@Html.DropDownList("CurveId", new SelectList(Model.AvailableCurveId, Model.CurveId), selectText)
 
 <img id="chart"/>
+<span class="help-block">
+    <span id="chart-error"></span>
+</span>
 
 @section Scripts
 {
@@ -15,17 +19,27 @@
         $(function () {
             $('#CurveId')
                 .change(function () {
+                    $('#chart-error').removeClass('text-danger').text('');
                     var $chart = $("#chart");
-                    var $spinner = $(this).after('<i class="fa fa-spinner fa-spin"></i>').next('i');
-                    $chart.attr('src', "");
+                    $chart.removeAttr('src');
+
                     var curveId = $("option:selected", this).text();
+                    if (curveId === "@Html.Raw(selectText)") {
+                        return;
+                    }
+                    var $spinner = $(this).after('<i class="fa fa-spinner fa-spin"></i>').next('i');
                     var url =
                         "@Html.Raw(Url.Action("ChartCurve", new {leafInputId = Model.LeafInputId, curveId="curveId"}))";
                     url = url.replace("=curveId", "=" + curveId);
-                    $chart.attr('src', url)
-                        .load(function() {
+                    $chart.load(function () {
                             $spinner.remove();
-                        });
+                        })
+                        .error(function () {
+                            $chart.removeAttr('src');
+                            $spinner.remove();
+                            $('#chart-error').addClass('text-danger').text('A problem was encountered loading this chart.');
+                        })
+                        .attr('src', url);
                 });
         });
     </script>