I want to fix tiny bug with OSC9 handling

[dolzenko]

What do you want to change?

I want to fix tiny bug described in #13790 because this affects my daily work

Why do you want to make this change?

because this affects my daily work and mood - don't like seeing Invalid UTF-8 notifications many times per day, feels broken to me :)

I acknowledge that:

• I have read the Contributing Guide and understand the contribution process.
• I have read and agree to follow the AI Usage Policy.
• I wrote this vouch request myself, in my own voice, without AI generating it.

[dolzenko]

My proposed fix dolzenko@af0e701a

[jcollie]

!vouch