Fix the skip-ahead-distinct optimization so that it works with indexes that

have repeated columns with different collating sequences.

FossilOrigin-Name: ce1e2b88777e00a82c04abe5ba35eec81b5f324e462f099cd00b21054f369688

src/whereInt.h

@@ -124,6 +124,7 @@ struct WhereLoop {
       u16 nEq;               /* Number of equality constraints */
       u16 nBtm;              /* Size of BTM vector */
       u16 nTop;              /* Size of TOP vector */
+      u16 nIdxCol;           /* Index column used for ORDER BY */
       Index *pIndex;         /* Index used, or NULL */
     } btree;
     struct {               /* Information for virtual tables */