[GIT-PULLS] [php-src] PR #23426: sapi/lsapi: fix sapi_lsapi_ub_write() return value on short write

Pull Request: https://github.com/php/php-src/pull/23426
Author: lazerg

`sapi_lsapi_ub_write()` returns `str_length - ret` when `LSAPI_Write()` writes fewer bytes than requested. `LSAPI_Write()` already returns the number of bytes it wrote (`LSAPI_Write_r()` in lsapilib.c returns `p - pBuf`, or -1 on error), the same contract every other `ub_write` in this codebase follows, e.g. `sapi_cli_ub_write()` returns `ptr - str`. Subtracting that count from `str_length` gives the wrong value. Return `ret` instead.

Fixes #23424