preview: add simple fetch queue and wait for noxy response

Instead of just blindly fetch noxy requests, this adds a simple
fetch queue and waits until the pending response is done. It
continues with the next one in the queue  whichever seen first,
This is not in chronological order, but incoming event order
(incoming events from different relays are probably out of order).

src/main.js

@@ -168,16 +168,23 @@ const getNoxyUrl = (type, url, id, relay) => {
   return link;
 }
 
-function linkPreview(href, id, relay) {
-  if ((/\.(gif|jpe?g|png)$/i).test(href)) {
-    return elem('div', {},
-      [elem('img', {className: 'preview-image-only', loading: 'lazy', src: getNoxyUrl('data', href, id, relay).href})]
-    );
-  }
+const fetchQue = [];
+let fetchPending;
+const fetchNext = (href, id, relay) => {
   const noxy = getNoxyUrl('meta', href, id, relay);
   const previewId = noxy.searchParams.toString();
-  fetch(noxy.href)
-    .then(data => data.json ? data.json() : data)
+  if (fetchPending) {
+    fetchQue.push({href, id, relay});
+    return previewId;
+  }
+  fetchPending = fetch(noxy.href)
+    .then(data => {
+      if (data.status === 200) {
+        return data.json();
+      }
+      // fetchQue.push({href, id, relay}); // could try one more time
+      return Promise.reject(data);
+    })
     .then(meta => {
       const container = document.getElementById(previewId);
       container.append(elem('a', {href, rel: 'noopener noreferrer', target: '_blank'}, [
@@ -189,7 +196,24 @@ function linkPreview(href, id, relay) {
       ]));
       container.classList.add('preview-loaded');
     })
+    .finally(() => {
+      fetchPending = false;
+      if (fetchQue.length) {
+        const {href, id, relay} = fetchQue.shift();
+        return fetchNext(href, id, relay);
+      }
+    })
     .catch(console.warn);
+  return previewId;
+};
+
+function linkPreview(href, id, relay) {
+  if ((/\.(gif|jpe?g|png)$/i).test(href)) {
+    return elem('div', {},
+      [elem('img', {className: 'preview-image-only', loading: 'lazy', src: getNoxyUrl('data', href, id, relay).href})]
+    );
+  }
+  const previewId = fetchNext(href, id, relay);
   return elem('div', {
     className: 'preview',
     id: previewId