SIO-1303 Internal Error when uploading a sinolpack with wrongly encoded Polish letters in the title

Changed unicode() to smart_str() when printing exception message to the form. Unicode(exception) fails when message has non-ASCII characters.

Change-Id: Id020a62a760fff78f7422cd2c516b41b1fe5d7d2
Merge "SIO-1303 Internal Error when uploading a sinolpack with wrongly encoded Polish letters in the title"