Fix downloads for shared depots that provide their own manifests.

Before, we could only do shared depots that referred to their parent app,
when parent app access was also available.

DepotDownloader/ContentDownloader.cs

@@ -208,7 +208,10 @@ namespace DepotDownloader
             if (depotChild == KeyValue.Invalid)
                 return INVALID_MANIFEST_ID;
 
-            if (depotChild["depotfromapp"] != KeyValue.Invalid)
+            // Shared depots can either provide manifests, or leave you relying on their parent app.
+            // It seems that with the latter, "sharedinstall" will exist (and equals 2 in the one existance I know of).
+            // Rather than relay on the unknown sharedinstall key, just look for manifests. Test cases: 111710, 346680.
+            if (depotChild["manifests"] == KeyValue.Invalid && depotChild["depotfromapp"] != KeyValue.Invalid)
             {
                 uint otherAppId = (uint)depotChild["depotfromapp"].AsInteger();
                 if (otherAppId == appId)