Merge branch 'jk/commit-C-pick-empty' into maint

"git commit --allow-empty-message -C $commit" did not work when the
commit did not have any log message.

* jk/commit-C-pick-empty:
commit: do not complain of empty messages from -C

diff --cc builtin/commit.c
index 9cfef6c6cca61973a4982763e4b834bf1b45cb75,aa04507174765a230ff56626cffb5d0a7e66c4a7..65c069d2cbdd7f34b9ebf7add06e65de17df8efa
--- 1/builtin/commit.c
--- 2/builtin/commit.c
+++ b/builtin/commit.c
@@@ -648,11 -649,9 +648,10 @@@ static int prepare_to_commit(const cha
                                  logfile);
                hook_arg1 = "message";
        } else if (use_message) {
 +              char *buffer;
                buffer = strstr(use_message_buffer, "\n\n");
-               if (!use_editor && (!buffer || buffer[2] == '\0'))
-                       die(_("commit has empty message"));
-               strbuf_add(&sb, buffer + 2, strlen(buffer + 2));
+               if (buffer)
+                       strbuf_add(&sb, buffer + 2, strlen(buffer + 2));
                hook_arg1 = "commit";
                hook_arg2 = use_message;
        } else if (fixup_message) {