BUGZILLA-1111383 Don't assume that 'kind' is a valid key

'kind' is not necessarily emitted during a declDef record creation,
so we should provide a default value of None to avoid crashing.

https://bugzilla.mozilla.org/show_bug.cgi?id=1111383
I believe that type_menu can also be called with a 'decldef'

https://github.com/mozilla/dxr/blob/es/dxr/plugins/clang/indexers.py#L132

Which does not necessarily emit a 'kind' record.

https://github.com/mozilla/dxr/blob/es/dxr/plugins/clang/dxr-index.cpp#L346-L359

Let me know if I'm misunderstanding the code.