fix: SIGSEGV when call after closed

When close called, a resource which handle points is freed in libhunspell, but handle does not become null. There are null checks in spell and add methods. But they are non-sense because handle is always not null, and suggest method don't have the check.

This fix the issue with set handle to null when closed, and check null in a suggest method.

The bug is reported on downstream project languagetool and its user OmegaT application.

Ref: languagetool project issue and pull-request ticket https://github.com/languagetool-org/languagetool/pull/8772

Ref: OmegaT project issue ticket https://sourceforge.net/p/omegat/bugs/1182/

Signed-off-by: Hiroshi Miura miurahr@linux.com