Better fallbacks

src/components/custom-emoji.jsx

@@ -1,9 +1,11 @@
 export default function CustomEmoji({ staticUrl, alt, url }) {
   return (
     <picture>
-      <source srcset={staticUrl} media="(prefers-reduced-motion: reduce)" />
+      {staticUrl && (
+        <source srcset={staticUrl} media="(prefers-reduced-motion: reduce)" />
+      )}
       <img
-        key={alt}
+        key={alt || url}
         src={url}
         alt={alt}
         class="shortcode-emoji emoji"