Bugfix when handling requests with empty body

[dhm80]

If you call a page with e. g. Method GET and ContentType text/xml the method getParsedBody() throws an Exception as $this->bodyis always set (as it contains a StreamInterface) if the body is empty.

The correct procedure would be to check if the body has content.

[coveralls]

Coverage remained the same at 97.954% when pulling afe1b95 on dhm80:patch-1 into c138554 on slimphp:3.x.

[akrabat]

Please create a unit test and supply a curl command that shows the problem.

Thanks.

[akrabat]

I can't reproduce with this test:

    public function testGetParsedBodyXmlWithNoBody()
    {
        $method = 'GET';
        $uri = new Uri('https', 'example.com', 443);
        $headers = new Headers();
        $headers->set('Content-Type', 'application/xml');
        $cookies = [];
        $serverParams = [];
        $body = new RequestBody();
        $body->write('');
        $request = new Request($method, $uri, $headers, $cookies, $serverParams, $body);

        $this->assertEquals('', $request->getParsedBody());
    }

Please write a test that shows the problem and add to this branch and then reopen the PR.