added missing space in the sandbox attribute

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

@@ -1014,7 +1014,7 @@ this.SingleFileCore = this.SingleFileCore || (() => {
 								frameElement.removeAttribute(docUtil.WIN_ID_ATTRIBUTE_NAME);
 								let sandbox = "allow-popups allow-top-navigation allow-top-navigation-by-user-activation";
 								if (pageData.content.match(NOSCRIPT_TAG_FOUND) || pageData.content.match(SCRIPT_TAG_FOUND)) {
-									sandbox += "allow-scripts allow-same-origin";
+									sandbox += " allow-scripts allow-same-origin";
 								}
 								frameElement.setAttribute("sandbox", sandbox);
 								if (frameElement.tagName == "OBJECT") {