withCasing() must return or throw

[TinoDidriksen]

I: Program returns random data in a function
E: libdivvun no-return-in-nonvoid-function suggest.hpp:158

Function withCasing() on https://github.com/divvun/libdivvun/blob/master/src/suggest.hpp#L144 must do something at the end. If it's never supposed to reach that, throw a dummy exception - even just throw 1 will do.

[unhammer]

Committed, though should it be possible to reach the end when compiled with -Werror=switch?