providers/enchant_nuspell.cpp: fix a few leaks
providers/enchant_nuspell.cpp: fix a few leaks

A malloced char * was being converted to std::string without freeing the
char * in a few places.

AbiWord/enchant,rrthomas/enchant,rrthomas/enchant,AbiWord/enchant,rrthomas/enchant,AbiWord/enchant,AbiWord/enchant,rrthomas/enchant