Fix cases where code in expr.c was failing to handle OOM failures that occurred while processing sub-select expressions.

FossilOrigin-Name: 62efe2eee34fdb147cc456290576d8fc3801487867c78aadd4485f85468d9ffc

test/exprfault.test

@@ -0,0 +1,35 @@
+# 2021 April 17
+#
+# 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.
+#
+#***********************************************************************
+# This file implements regression tests for SQLite library.
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+set testprefix exprfault
+
+do_execsql_test 1.0 {
+  CREATE TABLE t1(a);                 
+  CREATE TABLE t2(d);                 
+}
+faultsim_save_and_close
+
+do_faultsim_test 1.1 -faults oom* -prep {
+  faultsim_restore_and_reopen
+} -body {
+  execsql {
+    SELECT a = ( SELECT d FROM (SELECT d FROM t2) ) FROM t1 
+  }
+} -test {
+  faultsim_test_result {0 {}}
+}
+
+
+finish_test