[PATCH v2] sequencer: cleanup for gcc warning in non developer mode

["Carlo Marcelo Arenas Belón" <carenas@gmail.com>]

as shown by:

  sequencer.c: In function ‘write_basic_state’:
  sequencer.c:2392:37: warning: zero-length gnu_printf format string [-Wformat-zero-length]
     write_file(rebase_path_verbose(), "");

where write_file will create an empty file if told to write an empty string
as can be inferred by the previous call

the somehow more convoluted syntax works around the issue by providing a non
empty format string and is already being used for the abort safety file since
1e41229d96 ("sequencer: make sequencer abort safer", 2016-12-07)

Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
---

Notes:
    Changes in v2
    
     - Avoid change of behaviour as suggested by Junio

 sequencer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sequencer.c b/sequencer.c
index 8dd6db5a01..10f602c4d4 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -2335,7 +2335,7 @@ int write_basic_state(struct replay_opts *opts, const char *head_name,
 		write_file(rebase_path_quiet(), "\n");
 
 	if (opts->verbose)
-		write_file(rebase_path_verbose(), "");
+		write_file(rebase_path_verbose(), "%s", "");
 	if (opts->strategy)
 		write_file(rebase_path_strategy(), "%s\n", opts->strategy);
 	if (opts->xopts_nr > 0)
-- 
2.19.1