Improve use of lockfile API

Remove remaining double close(2)'s.  i.e. close() before
commit_locked_index() or commit_lock_file().

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/fast-import.c b/fast-import.c
index 82e9161..3609c24 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -1546,10 +1546,18 @@
 	}
 
 	dump_marks_helper(f, 0, marks);
-	fclose(f);
-	if (commit_lock_file(&mark_lock))
+	if (ferror(f) || fclose(f))
 		failure |= error("Unable to write marks file %s: %s",
 			mark_file, strerror(errno));
+	/*
+	 * Since the lock file was fdopen()'ed and then fclose()'ed above,
+	 * assign -1 to the lock file descriptor so that commit_lock_file()
+	 * won't try to close() it.
+	 */
+	mark_lock.fd = -1;
+	if (commit_lock_file(&mark_lock))
+		failure |= error("Unable to write commit file %s: %s",
+			mark_file, strerror(errno));
 }
 
 static int read_next_command(void)