Fix NullReferenceException in os_setlocale
Fix NullReferenceException in os_setlocale

os.setlocale() with no arguments crashes beautifully (or not-so-beautifully).

Failing test:
assert(os.setlocale() == 'C')

Stevie-O/SharpLua,Stevie-O/SharpLua,Stevie-O/SharpLua