fix: rare crash placing new bases

Crashes can occur in two cases:
1) If a mouseover triggers between base being named and
BuildNewBaseState destructor call.
2) If a mouseover triggers between confirm new base cancellation and
BuildNewBaseState destructor call.

Solution is to swap between globeHover handler and an empty handler as
necessary.
zero handler

Forget using an empty handler, you can simply zero it.
Merge pull request #554 from cfailde/newbase

fix: rare crash placing new bases