Fix TypeError by rotation

[Ludy87]

Description

Fixes the error in the PDF multitool when rotating all pages at the same time.

PdfContainer.js:182
Uncaught TypeError: this.pagesContainer.childNodes[i].querySelector is not a function
    at PdfContainer.rotateAll (PdfContainer.js:182:53)
    at HTMLButtonElement.onclick (multi-tool:679:100)

Checklist:

• I have read the Contribution Guidelines
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings

Contributor License Agreement

By submitting this pull request, I acknowledge and agree that my contributions will be included in Stirling-PDF and that they can be relicensed in the future under the MPL 2.0 (Mozilla Public License Version 2.0) license.

(This does not change the general open-source nature of Stirling-PDF, simply moving from one license to another license)