Fix adding a subscription (again)

Also ensured HTTP last modified date is parsed properly.

lib/Database.php

@@ -418,7 +418,7 @@ class Database {
                     $feed->favicon,
                     $feed->data->siteUrl,
                     $feed->data->date,
-                    $feed->resource->getLastModified(),
+                    \DateTime::createFromFormat("!D, d M Y H:i:s e", $feed->resource->getLastModified()),
                     $feed->resource->getEtag(),
                     $fetchUser,
                     $fetchPassword

lib/Feed.php

@@ -38,7 +38,7 @@ class Feed {
             // Grab the favicon for the feed; returns an empty string if it cannot find one.
             // Some feeds might use a different domain (eg: feedburner), so the site url is
             // used instead of the feed's url.
-            $this->favicon = (new Favicon)->find($siteUrl);
+            $this->favicon = (new Favicon)->find($feed->siteUrl);
         } catch (PicoFeedException $e) {
             throw new Feed\Exception($url, $e);
         }