make sure document.doctype is defined

lib/web/editor/editor-web.js

@@ -1015,7 +1015,7 @@ table {
 					} else {
 						document.insertBefore(contentDocument.doctype, document.documentElement);
 					}
-				} else {
+				} else if (document.doctype) {
 					document.doctype.remove();
 				}
 				contentDocument.querySelectorAll("noscript").forEach(element => {

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

@@ -1012,7 +1012,7 @@ table {
 				} else {
 					document.insertBefore(contentDocument.doctype, document.documentElement);
 				}
-			} else {
+			} else if (document.doctype) {
 				document.doctype.remove();
 			}
 			contentDocument.querySelectorAll("noscript").forEach(element => {