Brad House provided a fix for ares_save_options(): Apparently I overlooked

Brad House provided a fix for ares_save_options(): Apparently I overlooked
something with the ares_save_options() where it would try to do a malloc(0)
when no options of that type needed to be saved.  On most platforms, this was
fine because malloc(0) doesn't actually return NULL, but on AIX it does, so
ares_save_options would return ARES_ENOMEM.