prevent removing HEAD tag when saving selection

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

@@ -976,7 +976,7 @@ this.SingleFileCore = this.SingleFileCore || (() => {
 					});
 				}
 				element = element.parentElement;
-				if (element && element.parentElement && element.parentElement.tagName != "BODY") {
+				if (element && element.parentElement && element.parentElement.tagName != "BODY" && element.parentElement.tagName != "HTML") {
 					isolateParentElements(element.parentElement, element);
 				}
 			}