This issue is related to phpGH-22332:

> Let's assume we have a stream with 5 queued bytes. When calling fread($s, 1),
> the underlying buffered stream will request a chunk of up to 8192 bytes
> immediately, but only return the requested 1 byte back to the reader. If the
> reader then requests fread($s, 10), _php_stream_read() will first return
> anything that was buffered but not yet read.
>
> If the requested length exceeds the number of buffered bytes (as is the case
> above), another read call is issued. This call will return nothing, because
> the stream only provides 4 more readable bytes, all of which are buffered.
> php_openssl_handle_ssl_error() (called by php_openssl_sockop_io()) will then
> incorrectly set last_status to WANT_READ, even though we've already read the
> remaining data.
>
> Furthermore, stream_select() can cause the same issue via
> php_openssl_sockop_cast(castas: PHP_STREAM_AS_FD_FOR_SELECT), which pre-fills
> the read buffer on SSL_pending() > 0. The subsequent fread() will lead to the
> same condition as above.
>
> There's a second issue here. If the stream is blocking, the supplement read
> will block for the duration of the timeout. This will be addressed in a second
> PR.

This addresses the last paragraph. Avoid a blocking read when we already have
buffered data, as we may have reached the end of the stream and will wait in
vain.