Clean up the struct archive used for reading an archive in the handling

of @archive commands.  This bug should be harmless as long as you don't
use an excessive number of @archive commands.

MFC after:	1 week

usr.bin/tar/write.c

@@ -513,6 +513,7 @@ append_archive(struct bsdtar *bsdtar, struct archive *a, const char *filename)
 		    filename, archive_error_string(ina));
 		bsdtar->return_value = 1;
 	}
+	archive_read_finish(ina);
 
 	/* Note: If we got here, we saw no write errors, so return success. */
 	return (0);