Avoid passing null bytes in regular expression in Object\Image

Avoid passing null bytes in regular expression in Object\Image

- Remove capturing expression for A|B in favor of bracket syntax in regular expression since matches aren't used.
- Regular expressions have their own character escape notation including backslashes that need to be escaped in a PHP string.
- Actually address https://github.com/friendica/friendica/issues/13761#issuecomment-1949930922