autobatching bug fixed.

[cydur]

This bugfix addresses the problem I already found several years ago. See my comment to Issue #1582.
I don't think it really was the same problem as the original error described in this issue because my problem was in the backward step and now I think #1582 could have been a problem in the forward step.

In any case this change fixes my problem. And the problem was (autobatching = 1):

• A auto-batched "+" node was the first argument of an also auto-batched "*" node.
  In this case the backward step in exec.cc called node->backward() with the batch tensor as last argument instead of the correct sub-tensor of this batch.

[cydur]

Well, I don't think my change has anything to do with the continuous integration error
"ERROR conda.core.link:_execute(502): An error occurred while installing package 'defaults::charset-normalizer-2.0.4-pyhd3eb1b0_0'.
CondaError: Cannot link a source that does not exist. C:\Miniconda36-x64\Scripts\conda.exe"

Seems to be a problem in the build environment...