render default package image on error (#10061)

Author: martinrrm

src/NuGetGallery/App_Code/ViewHelpers.cshtml

@@ -162,6 +162,11 @@
     <text>onerror="this.src='@url'; this.onerror = null;"</text>
 }
 
+@helper PackageImageFallback()
+{
+    <text>onerror="this.className='package-icon img-responsive package-default-icon'; this.onerror = null;"</text>
+}
+
 @helper Option(string value, string label, string currentValue)
 {
     <option value="@value" @if (value == currentValue)

src/NuGetGallery/Views/Packages/DisplayPackage.cshtml

@@ -269,7 +269,7 @@
                         <h1>
                             <span class="pull-left">
                                 <img class="package-icon img-responsive @(PackageHelper.ShouldRenderUrl(Model.IconUrl) && Model.ShowDetailsAndLinks ? null : "package-default-icon")" aria-hidden="true" alt=""
-                                     src="@(PackageHelper.ShouldRenderUrl(Model.IconUrl) && Model.ShowDetailsAndLinks ? Model.IconUrl : null)" />
+                                     src="@(PackageHelper.ShouldRenderUrl(Model.IconUrl) && Model.ShowDetailsAndLinks ? Model.IconUrl : null)" @ViewHelpers.ImageFallback(Url.Absolute("~/Content/gallery/img/default-package-icon-256x256.png")) />
                             </span>
                             <span class="title">
                                 @Html.BreakWord(Model.Id)

src/NuGetGallery/Views/Shared/_ListPackage.cshtml

@@ -31,7 +31,7 @@
     <div class="row">
         <div class="col-sm-1 hidden-xs hidden-sm col-package-icon">
             <img class="package-icon img-responsive @(!PackageHelper.ShouldRenderUrl(Model.IconUrl) ? "package-default-icon" : null)" aria-hidden="true" alt=""
-                 src="@(PackageHelper.ShouldRenderUrl(Model.IconUrl) ? Model.IconUrl : null)" />
+                 src="@(PackageHelper.ShouldRenderUrl(Model.IconUrl) ? Model.IconUrl : null)" @ViewHelpers.PackageImageFallback()/>
         </div>
         <div class="col-sm-11">
             <div class="package-header">

src/NuGetGallery/Views/Users/_UserPackagesListForDeletedAccount.cshtml

@@ -44,7 +44,7 @@
                             </td>
                             <td class="align-middle hidden-xs">
                                 <img class="package-icon img-responsive @(!PackageHelper.ShouldRenderUrl(package.IconUrl) ? "package-default-icon" : null)" aria-hidden="true" alt="Package Icon"
-                                     src="@(PackageHelper.ShouldRenderUrl(package.IconUrl) ? package.IconUrl : null)" />
+                                     src="@(PackageHelper.ShouldRenderUrl(package.IconUrl) ? package.IconUrl : null)" @ViewHelpers.PackageImageFallback()/>
                             </td>
                             <td class="align-middle package-id"><a href="@Url.Package(package.Id)">@Html.BreakWord(package.Id.Abbreviate(40))</a></td>
                             <td class="align-middle">