[subtitles][libass] add fallback value for no PlayRes

[CastagnaIT]

Description

User provided a .ass subtitle without PlayResX / PlayResY values that usually must be provided
since the value is 0, cause a wrong behaviour in the scaling calculations

the calculated fallbacks values for PlayResX / PlayResY are specified here
https://github.com/libass/libass/blob/6a759836e5e76bb7b69b0ac244eea76b0d290512/libass/ass.c#L1782-L1795
since they are verified only when libass redering start, we cant get the corrected values

the fix consist in the imitate the libass sources behaviours and print to the log when this happens
i choosen to not copy libass sources 1:1 because has not much sense if the upstream change in future

Motivation and context

fix #23481

How has this been tested?

you can use test.zip
with any mkv with same file name

then enable/disable fonts override sub setting

What is the effect on users?

show text in the right place and not on top/outside of the screen

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