Don't raise if there is no matching entry

slapos/networkcachehelper.py

@@ -198,20 +198,19 @@ def helper_download_network_cached(dir_url, cache_url,
         matching_entry_list.append(tags)
       except Exception:
         pass
+    if matching_entry_list:
     # If a strategy is defined, call it to determine best entry
-    if strategy:
-      best_entry = strategy(matching_entry_list)
-      if not best_entry:
-        logger.info("Can't find best entry matching strategy, selecting "
-            "random one between acceptable ones.")
+      if strategy:
+        best_entry = strategy(matching_entry_list)
+        if not best_entry:
+          logger.info("Can't find best entry matching strategy, selecting "
+              "random one between acceptable ones.")
+          best_entry = matching_entry_list[0]
+      else:
         best_entry = matching_entry_list[0]
-    else:
-      best_entry = matching_entry_list[0]
-
-    # download best entry
-    file_descriptor = nc.download(best_entry.get('sha512'))
 
-    if file_descriptor is not None:
+      # download best entry
+      file_descriptor = nc.download(best_entry.get('sha512'))
       return file_descriptor, tags
     else:
       logger.info('No matching entry to download from network cache: %s'\