owfeaturecontructor: Fix an IndexError accessing exception's args
owfeaturecontructor: Fix an IndexError accessing exception's args

The exception's `args` member can be an empty tuple if an exception
is constructed without any arguments (neither is it necessarily a string
as the code assumed).

Use `traceback.format_exception_only` helper to display the exception
message. Also log the full stack trace for easier debugging.

cheral/orange3,cheral/orange3,cheral/orange3,cheral/orange3,cheral/orange3,cheral/orange3