Fix bug in addFeeds

addFeeds would stop if it encountered a url that we already had in the
database instead of continuing with the next one.  This bug was
introduced due to refactoring for sync.

src/datamanager.cpp

@@ -338,7 +338,7 @@ void DataManager::addFeeds(const QStringList &urls, const bool fetch)
         qCDebug(kastsDataManager) << "Adding feed";
         if (feedExists(url)) {
             qCDebug(kastsDataManager) << "Feed already exists";
-            return;
+            continue;
         }
         qCDebug(kastsDataManager) << "Feed does not yet exist";