Fix harmless Clang warning about unreachable code.

Unfortunately Clang intelligent flow analysis prevents us from using different
asserts for invalid parameter value and unhandled one, which could happen if
more elements are added to wxMouseButton enum in the future.

Closes #15201.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73972 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Whack-a-mole with wxOSX/PPC unit tests continued.

The problem was not related to float-to-double conversions in wxAny code, try
to narrow it even further.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73973 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775