python: Hack to not crash when the log function raises an exception

python: Hack to not crash when the log function raises an exception

If the log callback raises a Python exception, we cannot handle this in
the C code since there are not return values checked.

Instead, we will check now if an exception has occured and print it to
the console. Not great, but at least this is useful for debugging.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>