When flattening UNION ALL subqueries into a join query, ensure that separate cursor numbers are used for each segment of the newly flattened query.

FossilOrigin-Name: c510377b0b052e400f2ee4f20220b61cdf74ee44b9bb9e6490787c88dd4c55aa

test/unionallfault.test

@@ -25,9 +25,9 @@ do_faultsim_test 1 -faults oom-t* -prep {
   faultsim_restore_and_reopen
 } -body {
   execsql {
-    SELECT * FROM (
+    SELECT * FROM t1, (
       SELECT x FROM t1 UNION ALL SELECT y FROM t1
-    )
+    ), t3
   }
 } -test {
   faultsim_test_result {0 {}}