Per an observation from Thom Brown that the old version contained a typo.
if (!ConditionalLockBufferForCleanup(buf))
{
/*
- * It's OK to skip vacuuming a page, as long as its not got data
- * that needs to be cleaned for wraparound avoidance.
+ * If we're not scanning the whole relation to guard against XID
+ * wraparound, it's OK to skip vacuuming a page. The next vacuum
+ * will clean it up.
*/
if (!scan_all)
{