Bug report（问题描述）

转html为pdf报错，生成的pdf文件为空文档

Steps to reproduce（问题复现步骤）

wkhtmltopdf --debug-javascript --no-stop-slow-scripts https://panjiachen.github.io/vue-element-admin/#/ 1223.pdf

Screenshot or Gif（截图或动态图）

[root@iZbp1erlsv2qdmc7sx22taZ ftpuser]# wkhtmltopdf --debug-javascript --no-stop-slow-scripts https://panjiachen.github.io/vue-element-admin/#/ 1223.pdf
Loading pages (1/6)
Warning: undefined:0 TypeError: 'undefined' is not a function
Counting pages (2/6)
Resolving links (4/6)
Loading headers and footers (5/6)
Printing pages (6/6)
Done

Link to minimal reproduction（最小可在线还原demo）

Other relevant information（格外信息）

os:win7
node version: V10.14.2
vue:3.2.1
wkhtmltopdf:0.12.5 (with patched qt)