phpseclib\Crypt\RSA::loadKey result not checked

[ben-challis]

Currently League\Flysystem\Sftp\SftpAdapter::getPrivateKey() does not check the bool result of RSA::loadKey() where false indicates error.

flysystem-sftp/src/SftpAdapter.php

Lines 266 to 280 in 518ac7d

	public function getPrivateKey()
	{
	if ("---" !== substr($this->privateKey, 0, 3) && is_file($this->privateKey)) {
	$this->privateKey = file_get_contents($this->privateKey);
	}
	$key = new RSA();
	if ($password = $this->getPassword()) {
	$key->setPassword($password);
	}
	$key->loadKey($this->privateKey);
	return $key;

I hit this due to phpseclib/phpseclib#1372 where by regular OpenSSH generated keys wouldn't load when generated with recent versions.

Is it fair to say that this should be detected and a LogicException raised to ease identification of the problem? At present you end up with the general "Could not login ..." exception.