git_futils_writebuffer: default only when flags==0

Only use defaults for `git_futils_writebuffer` when flags == 0, lest
(1 << 31) be treated as the defaults.

src/fileops.c

@@ -237,14 +237,14 @@ int git_futils_writebuffer(
 {
 	int fd, do_fsync = 0, error = 0;
 
+	if (!flags)
+		flags = O_CREAT | O_TRUNC | O_WRONLY;
+
 	if ((flags & O_FSYNC) != 0)
 		do_fsync = 1;
 
 	flags &= ~O_FSYNC;
 
-	if (flags <= 0)
-		flags = O_CREAT | O_TRUNC | O_WRONLY;
-
 	if (!mode)
 		mode = GIT_FILEMODE_BLOB;
 

src/rebase.c

@@ -447,8 +447,8 @@ static int rebase_setupfiles_merge(git_rebase *rebase)
 	size_t i;
 	int error = 0;
 
-	if ((error = rebase_setupfile(rebase, END_FILE, -1, "%" PRIuZ "\n", git_array_size(rebase->operations))) < 0 ||
-		(error = rebase_setupfile(rebase, ONTO_NAME_FILE, -1, "%s\n", rebase->onto_name)) < 0)
+	if ((error = rebase_setupfile(rebase, END_FILE, 0, "%" PRIuZ "\n", git_array_size(rebase->operations))) < 0 ||
+		(error = rebase_setupfile(rebase, ONTO_NAME_FILE, 0, "%s\n", rebase->onto_name)) < 0)
 		goto done;
 
 	for (i = 0; i < git_array_size(rebase->operations); i++) {
@@ -459,7 +459,7 @@ static int rebase_setupfiles_merge(git_rebase *rebase)
 
 		git_oid_fmt(id_str, &operation->id);
 
-		if ((error = rebase_setupfile(rebase, commit_filename.ptr, -1,
+		if ((error = rebase_setupfile(rebase, commit_filename.ptr, 0,
 				"%.*s\n", GIT_OID_HEXSZ, id_str)) < 0)
 			goto done;
 	}
@@ -486,10 +486,10 @@ static int rebase_setupfiles(git_rebase *rebase)
 		rebase->orig_head_name;
 
 	if (git_repository__set_orig_head(rebase->repo, &rebase->orig_head_id) < 0 ||
-		rebase_setupfile(rebase, HEAD_NAME_FILE, -1, "%s\n", orig_head_name) < 0 ||
-		rebase_setupfile(rebase, ONTO_FILE, -1, "%.*s\n", GIT_OID_HEXSZ, onto) < 0 ||
-		rebase_setupfile(rebase, ORIG_HEAD_FILE, -1, "%.*s\n", GIT_OID_HEXSZ, orig_head) < 0 ||
-		rebase_setupfile(rebase, QUIET_FILE, -1, rebase->quiet ? "t\n" : "\n") < 0)
+		rebase_setupfile(rebase, HEAD_NAME_FILE, 0, "%s\n", orig_head_name) < 0 ||
+		rebase_setupfile(rebase, ONTO_FILE, 0, "%.*s\n", GIT_OID_HEXSZ, onto) < 0 ||
+		rebase_setupfile(rebase, ORIG_HEAD_FILE, 0, "%.*s\n", GIT_OID_HEXSZ, orig_head) < 0 ||
+		rebase_setupfile(rebase, QUIET_FILE, 0, rebase->quiet ? "t\n" : "\n") < 0)
 		return -1;
 
 	return rebase_setupfiles_merge(rebase);
@@ -821,8 +821,8 @@ static int rebase_next_merge(
 	normalize_checkout_options_for_apply(&checkout_opts, rebase, current_commit);
 
 	if ((error = git_indexwriter_init_for_operation(&indexwriter, rebase->repo, &checkout_opts.checkout_strategy)) < 0 ||
-		(error = rebase_setupfile(rebase, MSGNUM_FILE, -1, "%" PRIuZ "\n", rebase->current+1)) < 0 ||
-		(error = rebase_setupfile(rebase, CURRENT_FILE, -1, "%.*s\n", GIT_OID_HEXSZ, current_idstr)) < 0 ||
+		(error = rebase_setupfile(rebase, MSGNUM_FILE, 0, "%" PRIuZ "\n", rebase->current+1)) < 0 ||
+		(error = rebase_setupfile(rebase, CURRENT_FILE, 0, "%.*s\n", GIT_OID_HEXSZ, current_idstr)) < 0 ||
 		(error = git_merge_trees(&index, rebase->repo, parent_tree, head_tree, current_tree, &rebase->options.merge_options)) < 0 ||
 		(error = git_merge__check_result(rebase->repo, index)) < 0 ||
 		(error = git_checkout_index(rebase->repo, index, &checkout_opts)) < 0 ||