fix error handling in mix
fix error handling in mix

gintenlabo/jubatus_core,gintenlabo/jubatus_core,jubatus/jubatus,gintenlabo/jubatus,kumagi/jubatus_core,gintenlabo/jubatus,kmaehashi/jubatus,kumagi/jubatus_core,kmaehashi/jubatus_core,rimms/jubatus_core,rimms/jubatus_core,jubatus/jubatus,Asuka52/jubatus,rimms/jubatus_core,gintenlabo/jubatus_core,kmaehashi/jubatus_core,rimms/jubatus,kumagi/jubatus_core,jubatus/jubatus,mathn/jubatus,elkingtonmcb/jubatus,kumagi/jubatus_core,mathn/jubatus,rimms/jubatus_core,roselleebarle04/jubatus,elkingtonmcb/jubatus,roselleebarle04/jubatus,gintenlabo/jubatus_core,kmaehashi/jubatus_core,kmaehashi/jubatus,Asuka52/jubatus,rimms/jubatus,kmaehashi/jubatus_core