create_branch: move msg setup closer to point of use

In create_branch() we write the reflog msg into a buffer in
the main function, but then use it only inside a
conditional. If you carefully follow the logic, you can
confirm that we never use the buffer uninitialized nor write
when it would not be used. But we can make this a lot more
obvious by simply moving the write step inside the
conditional.

Signed-off-by: Jeff King <peff@peff.net>

branch.c

@@ -234,7 +234,7 @@ void create_branch(const char *name, const char *start_name,
 {
 	struct commit *commit;
 	unsigned char sha1[20];
-	char *real_ref, msg[PATH_MAX + 20];
+	char *real_ref;
 	struct strbuf ref = STRBUF_INIT;
 	int forcing = 0;
 	int dont_change_ref = 0;
@@ -290,19 +290,20 @@ void create_branch(const char *name, const char *start_name,
 		die(_("Not a valid branch point: '%s'."), start_name);
 	hashcpy(sha1, commit->object.oid.hash);
 
-	if (forcing)
-		snprintf(msg, sizeof msg, "branch: Reset to %s",
-			 start_name);
-	else if (!dont_change_ref)
-		snprintf(msg, sizeof msg, "branch: Created from %s",
-			 start_name);
-
 	if (reflog)
 		log_all_ref_updates = LOG_REFS_NORMAL;
 
 	if (!dont_change_ref) {
 		struct ref_transaction *transaction;
 		struct strbuf err = STRBUF_INIT;
+		char msg[PATH_MAX + 20];
+
+		if (forcing)
+			snprintf(msg, sizeof msg, "branch: Reset to %s",
+				 start_name);
+		else
+			snprintf(msg, sizeof msg, "branch: Created from %s",
+				 start_name);
 
 		transaction = ref_transaction_begin(&err);
 		if (!transaction ||