Changed content filters to show "unknown" if a deleted tag/author is selected

refs https://github.com/TryGhost/Ghost-Admin/pull/1474

- show some indicitive text rather than a blank dropdown button when type/author/tag/order query param is present but doesn't match something in our data sets (eg, if a tag/author has been deleted or a query param has been incorrectly typed)

app/controllers/posts.js

@@ -65,12 +65,12 @@ export default Controller.extend({
 
     selectedType: computed('type', function () {
         let types = this.get('availableTypes');
-        return types.findBy('value', this.get('type'));
+        return types.findBy('value', this.get('type')) || {value: '!unknown'};
     }),
 
     selectedOrder: computed('order', function () {
         let orders = this.get('availableOrders');
-        return orders.findBy('value', this.get('order'));
+        return orders.findBy('value', this.get('order')) || {value: '!unknown'};
     }),
 
     _availableTags: computed(function () {
@@ -82,7 +82,6 @@ export default Controller.extend({
             .filter(tag => tag.get('id') !== null)
             .sort((tagA, tagB) => tagA.name.localeCompare(tagB.name, undefined, {ignorePunctuation: true}));
         let options = tags.toArray();
-
         options.unshiftObject({name: 'All tags', slug: null});
 
         return options;
@@ -92,7 +91,7 @@ export default Controller.extend({
         let tag = this.get('tag');
         let tags = this.get('availableTags');
 
-        return tags.findBy('slug', tag);
+        return tags.findBy('slug', tag) || {slug: '!unknown'};
     }),
 
     _availableAuthors: computed(function () {
@@ -112,7 +111,7 @@ export default Controller.extend({
         let author = this.get('author');
         let authors = this.get('availableAuthors');
 
-        return authors.findBy('slug', author);
+        return authors.findBy('slug', author) || {slug: '!unknown'};
     }),
 
     actions: {

app/templates/components/gh-contentfilter.hbs

@@ -13,7 +13,7 @@
         data-test-type-select="true"
         as |type|
     >
-        {{type.name}}
+        {{#if type.name}}{{type.name}}{{else}}<span class="red">Unknown type</span>{{/if}}
     </PowerSelect>
     {{/unless}}
 
@@ -32,7 +32,7 @@
         data-test-author-select="true"
         as |author|
     >
-        {{author.name}}
+        {{#if author.name}}{{author.name}}{{else}}<span class="red">Unknown author</span>{{/if}}
     </PowerSelect>
     {{/unless}}
 
@@ -52,7 +52,7 @@
         data-test-tag-select="true"
         as |tag|
     >
-        {{tag.name}}
+        {{#if tag.name}}{{tag.name}}{{else}}<span class="red">Unknown tag</span>{{/if}}
     </PowerSelect>
     {{/unless}}
 
@@ -69,6 +69,6 @@
         @data-test-order-select="true"
         as |order|
     >
-        {{order.name}}
+        {{#if order.name}}{{order.name}}{{else}}<span class="red">Unknown</span>{{/if}}
     </PowerSelect>
 </div>