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For queries with derived tables populated having some side-effect, we
will fill such a derived table more than once, but without clearing
its rows.  Consequently it will have duplicate rows.
An example query exhibiting the problem is
  SELECT STRAIGHT_JOIN c1 FROM t1 JOIN (SELECT @A := 0) x;
Since mysql_derived_fill will, for UNCACHEABLE_DEPENDENT tables, drop
all rows and repopulate, we relax the condition at line 1204: rather
than assume all uncacheable values prevent early return, we now
allow an early return for uncacheable values other than
UNCACHEABLE_DEPENDENT.  In general, we only populate derived tables
once unless they're dependent tables.