Replace variable Index.avgEq (average number of rows in keys for which there is no sample in sqlite_stat4) with vector Index.aAvgEq.

FossilOrigin-Name: 7b70b419c43b2c3b2daf11d833a1d60245bfaef5
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index e2bcaaf..19b0d55 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -1551,7 +1551,7 @@
   unsigned uniqNotNull:1;  /* True if UNIQUE and NOT NULL for all columns */
 #ifdef SQLITE_ENABLE_STAT4
   int nSample;             /* Number of elements in aSample[] */
-  tRowcnt avgEq;           /* Average nEq value for key values not in aSample */
+  tRowcnt *aAvgEq;         /* Average nEq values for keys not in aSample */
   IndexSample *aSample;    /* Samples of the left-most key */
 #endif
 };