`subtitle: ...` is silently ignored if title is not present

[GegznaV]

Bug description

subtitle: ... is ignored if the title is not present. YAML:

subtitle: Subtitle
jupyter: python3

Output

The issue is not present with the following YAML:

---  
title: Project
subtitle: Subtitle
jupyter: python3
---

Then output:

I use Windows 10, VS Code and

Expected behavior

1. Either fix the issue (show the toolbar) in both situations
2. Or produce a clear warning that some setup options are ignored and provide an example of how to get the desired outcome.

Checklist

• Please include a minimal, fully reproducible example in a single .qmd file? Please provide the whole file rather than the snippet you believe is causing the issue.
• Please format your issue so it is easier for us to read the bug report.
• Please document the RStudio IDE version you're running (if applicable), by providing the value displayed in the "About RStudio" main menu dialog?
• Please document the operating system you're running. If on Linux, please provide the specific distribution.