Fixed incorrect member count and capitalisation in publish options for editors/authors

no issue

- `{{format-number}}` was showing "0" when passed in an empty/nullish string when it should have been showing nothing
- used `{{if-empty}}` to fix capitalisation when the member count is missing
  - previously attempted a CSS-only fix with `:first-letter` and `text-transform: uppercase` but that broke the layout in Safari

ghost/admin/app/components/editor-labs/modals/publish-flow/options.hbs

@@ -48,12 +48,14 @@
                                 {{format-number countFetcher.count}}
 
                                 {{!-- @recipientType = none/free/paid/all/specific --}}
-                                {{if (not-eq @recipientType "all") @recipientType}}
+                                {{#let (if (not-eq @recipientType "all") @recipientType) as |recipientType|}}
+                                    {{if (is-empty countFetcher.count) (capitalize recipientType) recipientType}}
+                                {{/let}}
 
                                 {{#if @publishOptions.onlyDefaultNewsletter}}
-                                    {{gh-pluralize countFetcher.count "subscriber" without-count=true}}
+                                    {{gh-pluralize countFetcher.count (if (is-empty countFetcher.count) "Subscriber" "subscriber") without-count=true}}
                                 {{else}}
-                                    {{gh-pluralize countFetcher.count "subscriber" without-count=true}}
+                                    {{gh-pluralize countFetcher.count (if (is-empty countFetcher.count) "Subscriber" "subscriber") without-count=true}}
                                     of <span class="gh-selected-newsletter">{{@publishOptions.newsletter.name}}</span>
                                 {{/if}}
                             {{/let}}

ghost/admin/app/helpers/format-number.js

@@ -1,6 +1,10 @@
 import {helper} from '@ember/component/helper';
 
 export function formatNumber(number) {
+    if (number === '' || number === null || number === undefined) {
+        return;
+    }
+
     return Number(number).toLocaleString();
 }