[Video] Fix for #25097 and requested updates from #24720

[78andyp]

Description

This PR is twofold:

1. It fixes the issue reported in Starting file playback with keyboard Enter button is broken in master #25097.

When play from here or automatically play next item are selected then a playlsit is generated.
If this was done through Video -> Files, on items that weren't yet scanned into the database then there was no VideoInfoTag and therefore p->GetVideoInfoTag()->m_basePath was actually empty.

This corrects that.

2. Requested updates from devs

As detailed in 54a63d0

Motivation and context

How has this been tested?

Part 1 by @smp79 who kindly reported the original issue.

What is the effect on users?

Fix and code optimisation/clarity.

Screenshots (if appropriate):

Types of change

• Bug fix (non-breaking change which fixes an issue)
• Clean up (non-breaking change which removes non-working, unmaintained functionality)
• Improvement (non-breaking change which improves existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that will cause existing functionality to change)
• Cosmetic change (non-breaking change that doesn't touch code)
• Student submission (PR was done for educational purposes and will be treated as such)
• None of the above (please explain below)

Checklist:

• My code follows the Code Guidelines of this project
• My change requires a change to the documentation, either Doxygen or wiki
• I have updated the documentation accordingly
• I have read the Contributing document
• I have added tests to cover my change
• All new and existing tests passed

[ksooo]

As far as I can tell, this looks good.

[ksooo]

jenkins build this please