Fix an assertion failure triggered by a SELECT with a compound sub-query that

contains an incorrectly placed ORDER BY clause. This problem is just an
assert() failure - non-DEBUG builds are not affected. Problem found by
OSSFuzz.

FossilOrigin-Name: 823779d31eb09cda5effe747d9adb35e600a52d4274226586437f674e7824d91

src/select.c

@@ -3773,7 +3773,6 @@ static int flattenSubquery(
         pOrderBy->a[i].u.x.iOrderByCol = 0;
       }
       assert( pParent->pOrderBy==0 );
-      assert( pSub->pPrior==0 );
       pParent->pOrderBy = pOrderBy;
       pSub->pOrderBy = 0;
     }