fixup! add: use preload-index and fscache for performance

At the end of the add command, disable and free the fscache so that we
don't leak the memory and so that we can dump the fscache statistics.

Signed-off-by: Ben Peart <benpeart@microsoft.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

builtin/add.c

@@ -622,6 +622,7 @@ finish:
 		die(_("Unable to write new index file"));
 
 	dir_clear(&dir);
+	enable_fscache(0);
 	UNLEAK(pathspec);
 	return exit_status;
 }