Cleanup error message printing in minitar example

Cleanup error message printing in minitar example

* An error message should not be printed if EOF is reached in copy_data. However
  an error message should be printed if any other error is encountered.

* A newline should be printed in extract if an error message was printed.

* If a file name is printed in extract (verbose operation) it should be followed
  by a space incase there is an error message.

Signed-off-by: Paul Barker <paul@paulbarker.me.uk>