bug#52097: 28.0.50; Regression - posn-at-point returns wrong result if overlay is present

[Eli Zaretskii]

> From: Daniel Mendler <mail@daniel-mendler.de>
> Date: Thu, 25 Nov 2021 11:13:04 +0100
> 
> 1. emacs -Q
> 2. Create new buffer bug.el
> 3. Activate flymake-mode (for the overlay)
> 4. Enter "  invalid-ident" (note the spaces at the beginning)
> 5. Wait until the flymake overlay appears

The overlay doesn't seem to appear for me, for some reason.

Could you please post a recipe that doesn't require Flymake?  Surely,
creating an overlay doesn't require such heavy machinery?  I tried to
put a simple overlay with before-string in a buffer, but didn't see
any problem with the Y coordinate reported by posn-at-point, so I
guess there's a need in something special in that overlay.

Thanks.