Fix PHP 8.5 curl_close() deprecation and TypeError on failed curl_init()

[Buzka91]

• call curl_close() only on PHP < 8.0 (no-op since 8.0, deprecated since 8.5)
• do not pass false to curl_error() when curl_init() fails, which threw TypeError instead of NetworkException on PHP 8

[Buzka91]

Hi @maciejlew,

Could you take a look at this PR when you have a moment? It's a small, backward-compatible fix:

• curl_close() has been a no-op since PHP 8.0 and emits E_DEPRECATED on PHP 8.5, so it's now called only when PHP_VERSION_ID < 80000. PHP 7 behaviour is unchanged.
• When curl_init() fails, curl_error() was called with false, which throws a TypeError on PHP 8 instead of the intended NetworkException.

Since the library already declares PHP 8.5 support, every request made through the bundled cURL client currently triggers a deprecation notice on 8.5. We're running PHP 8.5 in production and use this as a workaround on our side for now. A patch release (e.g. 4.0.1) with this fix would let us drop the workaround.

Thanks for maintaining the library!