Correctly initialize the iSelectId of FROM clause terms that are a self

join of a reused materialized subquery.  Without this, the EXPLAIN QUERY PLAN
output for the query will identify the subquery using the uninitialized
(and arbitrary) iSelectId.

FossilOrigin-Name: 43c9ae371f6250fee98a7c4011726eff8ad37f5a97add4f490ac3a2dd501a0d2

test/with1.test

@@ -990,5 +990,19 @@ do_execsql_test 18.2 {
   SELECT 1 FROM xyz;
 } 1
 
+# EXPLAIN QUERY PLAN on a self-join of a CTE
+#
+do_execsql_test 19.1 {
+  DROP TABLE IF EXISTS t1;
+  CREATE TABLE t1(x);
+  EXPLAIN QUERY PLAN
+  WITH
+    x1(a) AS (values(100))
+  INSERT INTO t1(x)
+    SELECT * FROM (WITH x2(y) AS (SELECT * FROM x1) SELECT y+a FROM x1, x2);
+  SELECT * FROM t1;
+} {0 0 0 {SCAN SUBQUERY 1} 0 1 1 {SCAN SUBQUERY 1}}
+
+
 
 finish_test