Fix a bug in checking the return value of _get_key_value()

```
Purpose of code changes on this branch:
Fix an easy bug in handshake.py. This change will fix http://crbug.com/44792.

When reviewing my code changes, please focus on:


After the review, I'll merge this branch into:
/trunk

```

Original issue reported on code.google.com by `yutak@chromium.org` on 15 Jul 2010 at 5:53
