Fix FastCGI protocol segfault
Fix FastCGI protocol segfault

At least this fixed the FastCGI issue for me, I am not sure if I
implemented it the correct way as I was not diving deep into FCGI
protocol.

GDB output before this fix:

Thread 2.2 "QThread" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fffee1d0700 (LWP 7141)]
CWSGI:4f6071babf5378269e77ecfaadccbdfec731c346@entry=0x7fffe800cd40,
    data=0x7fffe8010538 "Status: 302\r\nContent-Type: text/html; charset=utf-8\r\nServer: cutelyst/2.0.0\r\nX-Robots-Tag: none\r\nReferrer-Policy: no-referrer, strict-origin-when-cross-origin\r\nContent-Security-Policy: default-src 'no"..., len=560) at /usr/src/debug/cutelyst-1.99.60git.1520736217.6be7b34/wsgi/protocolfastcgi.cpp:562
562                 fr.req1 = sid[1];

cutelyst/cutelyst,buschmann23/cutelyst,cutelyst/cutelyst,cutelyst/cutelyst,buschmann23/cutelyst,buschmann23/cutelyst