truthy check for empty string in NameScope()
truthy check for empty string in NameScope()

Summary:
As in name. LATTE translation team moving some code from Python 2 to 3 uncovered a case where comparison between unicode and str types leads NameScope('') to prepend a separator to the beginning of blob names. This fixes it.

Thank you so much to dzhulgakov for tracking down the cause of this so quickly!

Reviewed By: dzhulgakov

Differential Revision: D6766866

fbshipit-source-id: fbe46cff581f425ba10e8668400915ea40baab94

Yangqing/caffe2,caffe2/caffe2,xzturn/caffe2,xzturn/caffe2,xzturn/caffe2,xzturn/caffe2,Yangqing/caffe2,Yangqing/caffe2,Yangqing/caffe2,xzturn/caffe2,Yangqing/caffe2