reflog-walk: tell explicit --date=default from not having --date at all

Introduction of opt->date_mode_explicit was a step in the right direction,
but lost that crucial bit at the very end of the callchain, and the callee
could not tell an explicitly specified "I want *date* but in default format"
from the built-in default value passed when there was no --date specified.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

log-tree.c

@@ -493,10 +493,9 @@ void show_log(struct rev_info *opt)
 			 * graph info here.
 			 */
 			show_reflog_message(opt->reflog_info,
-				    opt->commit_format == CMIT_FMT_ONELINE,
-				    opt->date_mode_explicit ?
-					opt->date_mode :
-					DATE_NORMAL);
+					    opt->commit_format == CMIT_FMT_ONELINE,
+					    opt->date_mode,
+					    opt->date_mode_explicit);
 			if (opt->commit_format == CMIT_FMT_ONELINE)
 				return;
 		}