Fix gotchas that could cause crashes or worse

Addresses bug #209 I hope this should be all. Tests seem to still work. Related issues: * https://github.com/jeaye/ncurses-rs/issues/172 * https://github.com/RustSec/advisory-db/issues/106 * https://github.com/jeaye/ncurses-rs/issues/149 * https://github.com/jeaye/ncurses-rs/issues/125