safe_strncpy is similar to strncpy, but makes sure buffer is
null-terminated. Update most of project to use this updated function to
prevent illegal memory accesses.
This is mostly `NULL` -> `nullptr` in cpp files, but I only noticed
because `LanguagePack::GetObjectOverride` and
`LanguagePack::GetScenarioOverride` were returning false instead of real
pointer.
Also fixes some whitespaces, you can `w=1` to github's URL to make it
skip these.
