Cannot use -Z with streaming upload

Can we get gzip content encoding to work with streaming uploads? Right now it seems there is a bug on this code path:

```
$ echo hello there | gsutil cp -Z - gs://bucket/doh.txt
Copying from ...
Failure: int() argument must be a string or a number, not 'NoneType'.
```

Start by reproducing the `gsutil cp -Z - gs://bucket/doh.txt` command and trace the streaming upload path where the `NoneType` conversion occurs. Done means stdin uploads successfully with gzip content encoding and the resulting object is available at the requested destination.

Written by the indexing model from the issue text.