Segfault from TabularEditor + `edit_traits`

I ran into an odd segfault and was able to reduce it to this minimal reproduction.

```python
from traits.api import (
HasTraits, List, Unicode, Tuple
)
from traitsui.api import View, UItem, TabularEditor
from traitsui.tabular_adapter import TabularAdapter

class MyClass(HasTraits):
my_list = List(Tuple(Unicode))
selected_row = Tuple(Unicode)

traits_view = View(
UItem(
'my_list',
editor=TabularEditor(
selected_row='selected_row',
adapter=TabularAdapter(columns=['Features']),
),
),
)

if __name__=='__main__':
MyClass().edit_traits()

```

This segfaults for me on:

```
Enthought Deployment Manager -- https://www.enthought.com
Python 3.6.0 |Enthought, Inc. (x86_64)| (default, Mar 3 2017, 03:26:01)
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import traits
>>> traits.__version__
'5.1.1'
>>> import traitsui
>>> traitsui.__version__
'6.1.1'
```