rename_ref(): only print a warning when config-file update fails

If git_config_rename_section() fails, rename_ref() used to return 1, which
left HEAD pointing to an absent refs/heads file (since the actual renaming
had already occurred).

Signed-off-by: Lars Hjemli <hjemli@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

refs.c

@@ -835,7 +835,7 @@ int rename_ref(const char *oldref, const char *newref, const char *logmsg)
 		snprintf(oldsection, 1024, "branch.%s", oldref + 11);
 		snprintf(newsection, 1024, "branch.%s", newref + 11);
 		if (git_config_rename_section(oldsection, newsection) < 0)
-			return 1;
+			error("unable to update config-file");
 	}
 
 	return 0;