fix: fatal php shutdowns (#2293)
Fixes #2268 (and maybe others)
In that issue, a timeout during a `curl_multi` request leads to a fatal
error and bailout during `php_request_shutdown()`. After looking at the
[FPM](https://github.com/php/php-src/blob/9011bd31d7c26b2f255e550171548eb024d1e4ce/sapi/fpm/fpm/fpm_main.c#L1926)
implementation I realized it also wraps `php_request_shutdown()` with a
`zend_bailout`, which we don't. This PR wraps the shutdown function and
restarts ZTS in case of an unexpected bailout, which fixes #2268 and
prevents any potential crashes from bailouts during shutdown.
Still a draft since I think it might make sense to wrap the whole
request loop in a `zend_try`.
