create_distinct_group() may need some extra space, so do a similar counting
in setup_ref_array() to have enough space in st_select_lex::ref_pointer_array

Also: shrinking an existing ref_pointer_array, as introduced by 
WL#5953 - Optimize away useless subquery clauses
has to be reversed. The '*' wildcards are fixed in the prepare phase,
but not in the execute phase.