Cairn.info: Serialize requests; fix PDF attachment URL

- Serialize requests when translating multiple results (cf. #2983)
- Fix incorrect PDF attachment URL (always "undefined", because of
  taking a property of a string primitive)

Cairn.info.js

@@ -9,7 +9,7 @@
 	"inRepository": true,
 	"translatorType": 4,
 	"browserSupport": "gcsibv",
-	"lastUpdated": "2022-05-31 18:42:02"
+	"lastUpdated": "2023-10-23 08:08:57"
 }
 
 /*
@@ -80,11 +80,9 @@ function getSearchResults(doc, checkOnly) {
 async function doWeb(doc, url) {
 	if (await detectWeb(doc, url) == 'multiple') {
 		let items = await Zotero.selectItems(getSearchResults(doc, false));
-		if (items) {
-			await Promise.all(
-				Object.keys(items)
-					.map(url => requestDocument(url).then(scrape))
-			);
+		if (!items) return;
+		for (let url of Object.keys(items)) {
+			await scrape(await requestDocument(url));
 		}
 	}
 	else {
@@ -125,7 +123,7 @@ async function scrape(doc) {
 
 		if (pdfLink) {
 			item.attachments.push({
-				url: pdfLink.href,
+				url: pdfLink,
 				title: 'Full Text PDF',
 				mimeType: 'application/pdf'
 			});