catch error during pre-processing docs

lib/single-file/frame-tree/content/frame-tree.js

@@ -192,7 +192,11 @@ this.FrameTree = this.FrameTree || (() => {
 					const message = JSON.parse(event.data.substring(MESSAGE_PREFIX.length + 2));
 					if (message.method == "getDataRequest" && message.windowId == frameWinId) {
 						topWindow.removeEventListener("message", onMessage, false);
-						docHelper.preProcessDoc(frameDoc, frameWindow, message.options);
+						try {
+							docHelper.preProcessDoc(frameDoc, frameWindow, message.options);
+						} catch (error) {
+							/* ignored */
+						}
 						const content = docHelper.getDoctype(frameDoc) + frameDoc.documentElement.outerHTML;
 						const emptyStyleRulesText = docHelper.getEmptyStyleRulesText(frameDoc);
 						const canvasData = docHelper.getCanvasData(frameDoc);