Ensure TabGroup to handle bad GET parameter

TabGroups and thus TabViews and TabbedTableViews don't handle bad GET
params well.

Example:  project/volumes/?tab=<!--
results in a "ValueError: need more than 1 value to unpack" error.

Change-Id: I7faf4f8c1c5c1f0ea078615282e7a7fbae2384b2
Closes-Bug: 1291567
Merge "Ensure TabGroup to handle bad GET parameter"