Support NVDA >= 2018.3 - wx 4 (#15)

[JulienCochuyt]

Fixes #15

Remove reference to wx.PyDeadObjectError, replaced by RuntimeError as of wx 4.

There probably are more elegant/robust way of doing it than the proposed bare except, but this is functional for what it is worth.

[derekriemer]

Thanks for this. I fixed it independently, before discovering your PR. Feel free to submit PRs in the future, I'll try to get to them faster.