Additional corner-case fixes for the in-scan-vs-index or OP_SeekScan

optimization.

FossilOrigin-Name: ad5ab24ebd557e7af1d92ab3fbcb3747c04da5ad4ed779fb6391dc94042687dd

src/where.c

@@ -2536,7 +2536,7 @@ static int whereLoopAddBtreeIndex(
         /* "x IN (value, value, ...)" */
         nIn = sqlite3LogEst(pExpr->x.pList->nExpr);
       }
-      if( pProbe->hasStat1 ){
+      if( pProbe->hasStat1 && rLogSize>=10 ){
         LogEst M, logK, safetyMargin;
         /* Let:
         **   N = the total number of rows in the table
@@ -2555,7 +2555,8 @@ static int whereLoopAddBtreeIndex(
         ** a safety margin of 2 (LogEst: 10) that favors using the IN operator
         ** with the index, as using an index has better worst-case behavior.
         ** If we do not have real sqlite_stat1 data, always prefer to use
-        ** the index.
+        ** the index.  Do not bother with this optimization on very small
+        ** tables (less than 2 rows) as it is pointless in that case.
         */
         M = pProbe->aiRowLogEst[saved_nEq];
         logK = estLog(nIn);

src/wherecode.c

@@ -1809,12 +1809,7 @@ Bitmask sqlite3WhereCodeOneLoopStart(
 
       op = aStartOp[(start_constraints<<2) + (startEq<<1) + bRev];
       assert( op!=0 );
-      assert( op==OP_SeekGE
-           || (pLoop->wsFlags & WHERE_IN_SEEKSCAN)==0
-           || (db->flags & SQLITE_ReverseOrder)!=0 );
-      if( (pLoop->wsFlags & WHERE_IN_SEEKSCAN)!=0
-       && op==OP_SeekGE            /* OP_SeekScan only does forward scans */
-      ){
+      if( (pLoop->wsFlags & WHERE_IN_SEEKSCAN)!=0 && op==OP_SeekGE ){
         assert( regBignull==0 );
         /* TUNING:  The OP_SeekScan opcode seeks to reduce the number
         ** of expensive seek operations by replacing a single seek with