set duplicate to true if needed

lib/single-file/single-file-core.js

@@ -258,12 +258,15 @@ this.SingleFileCore = this.SingleFileCore || (() => {
 				try {
 					const result = await Download.getContent(resourceURL, { asDataURI, maxResourceSize: options.maxResourceSize, maxResourceSizeEnabled: options.maxResourceSizeEnabled });
 					indexResource = this.hashes.indexOf(result.hash);
+					let duplicate = Boolean(resourceRequests.length > 1);
 					if (indexResource == -1) {
 						indexResource = this.hashes.length;
 						this.hashes.push(result.hash);
+					} else {
+						duplicate = true;
 					}
 					onloadListener({ index: indexResource, url: resourceURL });
-					resourceRequests.forEach(resourceRequest => resourceRequest.resolve({ content: result.content, empty: result.empty, indexResource, duplicate: Boolean(resourceRequests.length > 1) }));
+					resourceRequests.forEach(resourceRequest => resourceRequest.resolve({ content: result.content, empty: result.empty, indexResource, duplicate }));
 				} catch (error) {
 					indexResource = indexResource + 1;
 					onloadListener({ index: indexResource, url: resourceURL });