Parallel bt build crashes when DSM_NONE

Hello.

I happend to find that server crashes during regtest when
DSM_NONE is enforced. The attached patch fixes that.

The cause is the fact that _bt_spools_heapscan runs
_bt_begin_parallel() even if dynamic_shared_memory_type is
DSM_NONE. It is because plan_create_index_workers() is ignoring
dynamic_shared_memory_type.

We can reproduce this by letting initdb set
dynamic_shared_memory_type=none regardless of actual
availability. (Second attached) and just "make check".

regards,

-- 
Kyotaro Horiguchi
NTT Open Source Software Center
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 740de49..3e8cd14 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -5825,7 +5825,8 @@ plan_create_index_workers(Oid tableOid, Oid indexOid)
     double        allvisfrac;
 
     /* Return immediately when parallelism disabled */
-    if (max_parallel_maintenance_workers == 0)
+    if (dynamic_shared_memory_type == DSM_IMPL_NONE ||
+        max_parallel_maintenance_workers == 0)
         return 0;
 
     /* Set up largely-dummy planner state */
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index 2efd3b7..876e153 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -871,6 +871,7 @@ choose_dsm_implementation(void)
 #ifdef HAVE_SHM_OPEN
     int            ntries = 10;
 
+    return "none";
     while (ntries > 0)
     {
         uint32        handle;