Support both 4.2 and older versions and fix an exception

[kwsxing]

Proposed changes

• Support both 4.2 and older versions
• Fix an exception when clicking File -> Defaults -> Save Startup File

Screenshots/Screencasts

Below is the exception in Blender 3.5 and 4.2:

[thanhph111]

Thank you so much for your contribution, and I apologize for the delayed response. Your work is incredibly valuable, especially with the need for regular updates to ensure compatibility with each new Blender release. Unfortunately, I've been away from Blender and its Python API for quite some time and don’t feel confident enough to review this PR thoroughly.

If possible, @b-init might be able to assist with the review. Thank you again, and I apologize for the inconvenience.

[j6k4m8]

without adding pressure @b-init and @thanhph111, I've taken a look and this passes my review ;) @kwsxing's code is what I'm currently running on my blender instance.