Fix export html/pdf problem in Qt 5.15.5 (#2199)
Fix export html/pdf problem in Qt 5.15.5 (#2199)

maybe related https://github.com/vnotex/vnote/issues/1942   export PDF cpu 100%

```
Critical:(markdownviewer.js:103) Uncaught TypeError: Failed to delete an indexed property from 'NodeList': Index property deleter is not supported.
[520896:520896:0801/171207.286744:INFO:CONSOLE(103)] "Uncaught TypeError: Failed to delete an indexed property from 'NodeList': Index property deleter is not supported.", source: file:///home/henices/.local/share/VNote/VNote/web/js/prism.js (103)
```
tamlok/vnote,tamlok/vnote,tamlok/vnote,tamlok/vnote,tamlok/vnote