widgets.log: avoid traceback when output is None

Avoid concatenating None and str when `out` is None.

Signed-off-by: David Aguilar <davvid@gmail.com>
widgets.search: fix unicode errors in search combobox

The strings we use for the search modes were being returned with a
bytestring str() cast.  These can be translated so ensure that we use a
proper unicode string.

Closes #273

Reported-by: Ｖ字龍(Vdragon) <pika1021@gmail.com>
Signed-off-by: David Aguilar <davvid@gmail.com>