Fixed incorrect locale saving in Core::vlogLnInternal().

[dev-karpov0]

There was a bug in function Core::vlogLnInternal(...) related to incorrect saving of the locale when utf8=true. It led to incorrect text output to the console after calling this function.

Reason: std::setlocale(), if success, returns a pointer to a new locale, not an old.

To recreate a bug:

1. print some string from script using non-latin symbols e.g. Cyrillic (cp1251)
2. Do something that make Core::vlogLnInternal(.utf8=true) call. (e.g. Input invalid command into console)
3. Print string again

[CLAassistant]

All committers have signed the CLA.

[Hual]

This should fix #643 #637 #617 and #583

[Y-Less]

Why was debug level filtering added as well via this?

[dev-karpov0]

That condition was not added but moved higher (before the _lock_locales() call). Otherwise, if condition were true, _unlock_locales() would not be called.