[php-src] PR #22967: ftp: use SSL_write_ex() in single_send() to fix signed/unsigned handling

Pull Request: https://github.com/php/php-src/pull/22967 Author: crystarm This continues #19912, adding a fix for the outstanding review comment from @ndossche that hadn't been addressed yet. The first commit here (by @zeff-ir) replaces SSL_write() with SSL_write_ex(), which reports success/failure via its own int return value while writing the number of bytes sent through a separate size_t* out-parameter — avoiding the conversion issue entirely and matching the OpenSSL API contract. The second commit finishes the fix requested in review: single_send() still narrowed its result to int on return (return (int)sent;), even though it now computes a size_t (from SSL_write_ex()) or an ssize_t (from my_send_wrapper_with_restart() in the non-SSL path). Returning ssize_t instead avoids a theoretical truncation/overflow for writes larger than INT_MAX, which could otherwise collide with the -1 error sentinel checked by the caller (my_send()) or corrupt its buffer pointer arithmetic. In case this PR is accepted, #19912 should be closed.