ensure `dataset` is defined (fix #1570)

src/core/content/content-bootstrap.js

@@ -73,7 +73,7 @@ if (globalThis.window == globalThis.top && location && location.href && (locatio
 }
 
 async function extractFile() {
-	if (document.documentElement.dataset.sfz !== undefined) {
+	if (document.documentElement.dataset && document.documentElement.dataset.sfz !== undefined) {
 		const data = await getContent();
 		document.querySelectorAll("#sfz-error-message").forEach(element => element.remove());
 		executeBootstrap(data);
@@ -366,7 +366,7 @@ function detectSavedPage(document) {
 	if (savedPageDetected === undefined) {
 		const helper = singlefile.helper;
 		const firstDocumentChild = document.documentElement.firstChild;
-		compressContent = document.documentElement.dataset.sfz == "";
+		compressContent = document.documentElement.dataset && document.documentElement.dataset.sfz == "";
 		extractDataFromPageTags = Boolean(document.querySelector("sfz-extra-data"));
 		insertTextBody = Boolean(document.querySelector("body > main[hidden]"));
 		insertMetaCSP = Boolean(document.querySelector("meta[http-equiv=content-security-policy]"));

src/ui/content/content-ui-editor-web.js

@@ -2314,7 +2314,7 @@ pre code {
 			processNode(document);
 			reflowNotes();
 			document.querySelectorAll(${JSON.stringify(NOTE_TAGNAME)}).forEach(noteElement => attachNoteListeners(noteElement));
-			if (document.documentElement.dataset.sfz !== undefined) {
+			if (document.documentElement.dataset && document.documentElement.dataset.sfz !== undefined) {
 				waitResourcesLoad().then(reflowNotes);
 			}
 		})()`);