http: Fix CSD https requests
http: Fix CSD https requests

If request_body is NULL, buf_error(request_body) will return -ENOMEM to
indicate an allocation failure.  This is a good thing if we just called
buf_alloc(), but it is a bad thing if we aren't actually passing in a
request_body pointer.

The CSD GET requests pass in a NULL request_body and request_body_type:

    result = do_https_request(vpninfo, "GET", NULL, NULL, &form_buf, 0);

so this change is needed to restore proper CSD operation.

Signed-off-by: Kevin Cernekee <3105dbb3dd63fbb4f6371cfb04adc6726f76c56b@gmail.com>

brandt/openconnect,liiir1985/openconnect,mtmiller/openconnect,chadcatlett/openconnect,lins05/openconnect,don-johnny/openconnect,cernekee/openconnect,nmav/openconnect-mine,liiir1985/openconnect,don-johnny/openconnect,brandt/openconnect,atyndall/openconnect,nmav/openconnect-mine,matlockx/openconnect,matlockx/openconnect,lins05/openconnect,lins05/openconnect,matlockx/openconnect,don-johnny/openconnect,mveplus/openconnect-client,liiir1985/openconnect,mveplus/openconnect-client,don-johnny/openconnect,liiir1985/openconnect,brandt/openconnect,nmav/openconnect-mine,mveplus/openconnect-client,atyndall/openconnect,mtmiller/openconnect,atyndall/openconnect,mtmiller/openconnect,cernekee/openconnect,mveplus/openconnect-client,atyndall/openconnect,chadcatlett/openconnect,nmav/openconnect-mine,mtmiller/openconnect,chadcatlett/openconnect,chadcatlett/openconnect,lins05/openconnect,cernekee/openconnect,matlockx/openconnect,brandt/openconnect,cernekee/openconnect