rPa5d8b2d5cfd6

Fix a PHP 8.1 deprecated use of preg_match with a NULL argument

Summary:
These calls are preventing users to browse subversion/mercurial repositories in PHP 8.1+.
Indeed, a similar bug affecting git repositories was already addressed in another commit
(rP6b8ec50148909938850b5acfd11725ae23a8e31b). This commit harmonize both DiffusionSvnRequest
and DiffusionMercurialRequest with DiffusionGitRequest

Fix T15607

Test Plan:
- Sign in
- Open a diffusion SVN/Mercurial repository
- You should not get a…