Homestyx hydra

R1:b4cfe56f03b4

Fix PHP 8.1 "ltrim(null)" exception which blocks rendering first Meme comment

Summary:
Since PHP 8.1, passing a null string to `ltrim(string $string)` is deprecated.

Thus first check if After and Below text are not null before trimming.

Closes T15379

Test Plan:
Applied this change; afterwards several times created a new Pholio mock and added a Meme comment. I could not reproduce the problem anymore (first meme comment in a mock always rendered correctly instead of showing an exception as comment).
Repository: R1 hydra
Commit Date: Jun 10 2023