Fix GH-16433: Large values for openssl_csr_sign() $days overflow

The `offset_sec` parameter of `X509_gmtime_adj()` expects a `long`, but
the `$days` parameter of `openssl_csr_sign()` a `

Fix GH-16433: Large values for openssl_csr_sign() $days overflow

The `offset_sec` parameter of `X509_gmtime_adj()` expects a `long`, but
the `$days` parameter of `openssl_csr_sign()` a `zend_long`. We must
avoid signed integer overflow (UB), but also must not silently truncate.
Thus we check the given `$days` for the permissible range, and bail out
otherwise.

Closes GH-16437.

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