🐛 Fixed crash when newly created images are dragged into a gallery

closes https://github.com/TryGhost/Team/issues/1020

- image card payloads should have a valid `src` attribute, use that instead of relying on the associated `img` element which won't be found/have an unexpected `src` when it's newly created because the image card will still be using the blob url generated for a preview whilst uploading

ghost/admin/lib/koenig-editor/addon/components/koenig-card-gallery.js

@@ -457,7 +457,7 @@ export default Component.extend({
                 payload.width = payload.width || img.naturalWidth;
                 payload.height = payload.height || img.naturalHeight;
                 if (!payload.fileName) {
-                    let url = new URL(img.src);
+                    let url = new URL(payload.src || img.src);
                     let fileName = url.pathname.match(/\/([^/]*)$/)[1];
                     payload.fileName = fileName;
                 }