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
Merge fix for "kind" KeyErrors while indexing. Fix bug 1111383. Close #376.