RSA: add note discussion source of openssl errors

phpseclib/Crypt/RSA.php

@@ -622,6 +622,7 @@ class Crypt_RSA
             $publickey = call_user_func_array(array($this, '_convertPublicKey'), array_values($this->_parseKey($publickey, CRYPT_RSA_PUBLIC_FORMAT_PKCS1)));
 
             // clear the buffer of error strings stemming from a minimalistic openssl.cnf
+            // https://github.com/php/php-src/issues/11054 talks about other errors this'll pick up
             while (openssl_error_string() !== false) {
             }