Bug fix: protect against absence of directory

We do not want a symbolic link `$tests_old_dir/Extract_component_nx_2`
to be created if directory `$tests_old_dir/Extract_component_nx_2`
does not exist.

Overlap/Analysis/tests.json

@@ -35,7 +35,7 @@
 	[
 	    [
 		"ln", "-sf", "$tests_old_dir/EGr2nd15md4np3/e_overestim.txt",
-		"$tests_old_dir/Extract_component_nx_2"
+		"--target-directory=$tests_old_dir/Extract_component_nx_2"
 	    ],
 	    [
 		"$src_dir/Overlap/Analysis/plot_components.py",