[Bug] Change to rendering of left nav (TOC) in DocFx 2.76.0 means Download PDF link missing

**Describe the bug**
If the left navigation panel (TOC) is not rendered, but PDF output is enabled, no Download PDF link is rendered (because Download PDF link was part of panel). This makes it appear like PDF download is not available.

**To Reproduce**
Steps to reproduce the behavior:
1. Build any site, with PDF output enabled, with DocFx 2.76.0 or 2.77.0
2. Navigate to home page of built site
3. Home page shows no left navigation panel (TOC) and no Download PDF link
4. Navigate to a page within the site with child pages, and the left navigation panel (TOC) including Download PDF link appears

**Expected behavior**
When a site is configured to output to PDF, and the default (modern) theme is used, a Download PDF link should be rendered on every page .

**Context:**
- OS: Windows
- Docfx version: 2.76.0 and 2.77.0

**Additional context**
This was working in DocFx 2.75.3, but in DocFx 2.76.0 a change was made resulting in the left navigation panel (TOC) not being rendered in some cases, including the home page (see #10011 and PR #9737).

This issue does not question the change to the left navigation panel rendering. This issue just highlights that the PDF download link needs to appear on all pages to make it obvious and accessible.

Maybe the PDF download link could be rendered in the footer (i.e. where the Previous and Next page links are) ??