parseCurlResponse() cannot take NULL body

[phil-davis]

https://drone.owncloud.com/owncloud/core/20613/25/10

PHPUnit 6.5.14 by Sebastian Bergmann and contributors.
Runtime: PHPDBG 7.1.30-1+ubuntu16.04.1+deb.sury.org+1
Configuration: /drone/src/tests/phpunit-autotest-external.xml
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Time: 8.17 seconds, Memory: 34.00MB
There were 85 errors:
1) OCA\Files_External\Tests\Storage\WebdavTest::testRoot
TypeError: Argument 2 passed to Sabre\HTTP\Client::parseCurlResponse() must be of the type string, null given, called in /drone/src/lib/composer/sabre/http/lib/Client.php on line 547
/drone/src/lib/composer/sabre/http/lib/Client.php:457
/drone/src/lib/composer/sabre/http/lib/Client.php:547
/drone/src/lib/composer/sabre/http/lib/Client.php:432
/drone/src/lib/composer/sabre/http/lib/Client.php:325
/drone/src/lib/composer/sabre/http/lib/Client.php:114
/drone/src/lib/composer/sabre/dav/lib/DAV/Client.php:372
/drone/src/lib/private/Files/Storage/DAV.php:678
/drone/src/lib/private/Files/Storage/DAV.php:188
/drone/src/apps/files_external/tests/Storage/WebdavTest.php:57

It looks like https://github.com/sabre-io/http/blob/5.0.1/lib/Client.php#L532

$responseBody = substr($response, $curlInfo['header_size']) ?: null;

can cause $responseBody to be NULL and that gets passed to

return $this->parseCurlResponse($headerBlob, $responseBody, $curlHandle);

but parseCurlResponse has:

    protected function parseCurlResponse(array $headerLines, string $body, $curlHandle): array

and in this case $body is null, not a string.

This "null body" edge case seems to have been missed in the refactoring done in PR #115

[phil-davis]

Probably this can be worked-around by adjusting the higher calling code to no longer use the deprecated parseCurlResult - but in theory that should not be necessary for a patch point release.

[phil-davis]

Duplicate of #124