extractor: Fix extraction of one file archives

Currently, an empty folder is created when extracting an archive over Nautilus which contains one file with the same name as the archive. This is because gnome-autoar always creates the top-level folder, but the one file archive with the same name should be extracted directly without creating additional folders. Otherwise the conflict signal is emitted and Nautilus by default skips conflicting files, so only empty folder remains after extraction. This problem have not been unfortunately noticed by the test-one-file-same-name unit test due to differences in the decide-destination signal handling. Let's do not create the top-level folder at all as g_file_make_directory_with_parents is used later anyway.

Fixes: #28 (closed)