fix segfault in GetKey when there is nill err object

This is specific fix in error handling, which is was later broadly addressed by #14 (closed) - so I close this one

Closes #13 (closed)

handler/handler.go

@@ -121,8 +121,8 @@ func (s *KeyStorageServerImpl) GetKey(ctx context.Context, in *api.GetKeyRequest
 		log.Println("No such key " + in.Uuid)
 		getKeyResponse.Key = nil
 		getKeyResponse.StatusList = utils.AddStatus(getKeyResponse.StatusList,
-			"500", api.StatusType_ERROR, err.Error())
-		return getKeyResponse, err
+			"500", api.StatusType_ERROR, "No such key " + in.Uuid)
+		return getKeyResponse, errors.New("No such key " + in.Uuid)
 	}
 
 	getKeyResponse.Key = key