Fix crash when backfill is not needed.

Author: cheatfate

beacon_chain/sync/sync_overseer2.nim

@@ -658,21 +658,23 @@ proc updateQueues(
     overseer.fsqueue.reset(
       overseer.getForwardSidecarStartSlot(), checkpoint.epoch.start_slot())
 
-  if not(overseer.bqueue.running()):
-    let
-      startSlot = dag.backfill.slot
-      finishSlot =
-        if dag.horizon >= startSlot:
-          startSlot
-        else:
-          dag.horizon
-    overseer.bqueue.reset(startSlot, finishSlot)
+  if not(isNil(overseer.bqueue)):
+    if not(overseer.bqueue.running()):
+      let
+        startSlot = dag.backfill.slot
+        finishSlot =
+          if dag.horizon >= startSlot:
+            startSlot
+          else:
+            dag.horizon
+      overseer.bqueue.reset(startSlot, finishSlot)
 
-  if not(overseer.bsqueue.running()):
-    let
-      startSlot = dag.backfill.slot
-      finishSlot = overseer.getBackfillSidecarFinalSlot()
-    overseer.bsqueue.reset(startSlot, finishSlot)
+  if not(isNil(overseer.bsqueue)):
+    if not(overseer.bsqueue.running()):
+      let
+        startSlot = dag.backfill.slot
+        finishSlot = overseer.getBackfillSidecarFinalSlot()
+      overseer.bsqueue.reset(startSlot, finishSlot)
 
 proc updateColumnStatistics(
     overseer: SyncOverseerRef2,