Allow sub-queries that use UNION ALL to be flattened, even if the parent query is a join. Still some problems on this branch.

FossilOrigin-Name: 00e4bf74d3dfb87666a2266905f7d1a2afc6eb088d22cfd4f38f048733d6b936

test/unionallfault.test

@@ -0,0 +1,36 @@
+# 2020-12-16
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#***********************************************************************
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+set testprefix unionallfault
+
+do_execsql_test 1.0 {
+  CREATE TABLE t1(x,y,z);
+  CREATE TABLE t3(x,y,z);
+}
+faultsim_save_and_close
+
+
+do_faultsim_test 1 -faults oom-t* -prep {
+  faultsim_restore_and_reopen
+} -body {
+  execsql {
+    SELECT * FROM (
+      SELECT x FROM t1 UNION ALL SELECT y FROM t1
+    )
+  }
+} -test {
+  faultsim_test_result {0 {}}
+}
+
+finish_test