Souin doesn't cache conditional request after cache miss

[K0tBegemot]

When using version 1.6.47, if browser or another tool send conditional request with If-None-Match header then souin request original (upstream) server on every request. In this case, the entry is not added to the cache. After the usual request (non conditional), entry is added to the cache and no further requests are sent to the original(upstream) server (if you make extra conditional requests). After that, I checked the Nginx cache behavior in this case. After receiving the first request, the response was cached successfully and no more requests were made (After receiving additional requests)(Within the ttl time of course). This looks like a bug to me. Any ideas?