--walk-reflogs: disallow uninteresting commits

Do not allow uninteresting commits with --walk-reflogs, since it is
not clear what should be shown in these cases:

	$ git log --walk-reflogs master..next
	$ git log --walk-reflogs ^master

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>

reflog-walk.c

@@ -145,6 +145,9 @@ void add_reflog_for_walk(struct reflog_walk_info *info,
 	char *branch, *at = strchr(name, '@');
 	struct commit_reflog *commit_reflog;
 
+	if (commit->object.flags & UNINTERESTING)
+		die ("Cannot walk reflogs for %s", name);
+
 	branch = xstrdup(name);
 	if (at && at[1] == '{') {
 		char *ep;