Improve the accuracy of the estimates used when searching an index for values not present in any stat4 samples under some circumstances.

FossilOrigin-Name: e6f7f97dbc677c9f01b23142928c3fa7307c2fba

src/sqliteInt.h

@@ -1801,6 +1801,7 @@ struct Index {
   int nSampleCol;          /* Size of IndexSample.anEq[] and so on */
   tRowcnt *aAvgEq;         /* Average nEq values for keys not in aSample */
   IndexSample *aSample;    /* Samples of the left-most key */
+  tRowcnt *aiRowEst;       /* Non-logarithmic stat1 data for this table */
 #endif
 };