[php-src] Issue #10101: realpath() with empty path should return false

Issue: https://github.com/php/php-src/issues/10101 Author: mvorisek ### Description All file functions, incl. dir functions like file_exists() or is_dir() return false when the input is empty. One exception is realpath(), it returns the current directory when '' is given. The reason is probably the way how realpath() is written, the path is probably checked if absolute and if not, it is appended to the current directory, even if empty. After a fix, I expect realpath('') to return false. ### PHP Version any ### Operating System any