eth/downloader: handle missing withdrawals if empty list is expected (#26675)

This PR relaxes the block body ingress handling a bit: if block body withdrawals are missing (but expected to be empty), the body withdrawals are set to 'empty list' before being passed to upper layers. 

This fixes an issue where a block passed from EthereumJS to geth was deemed invalid.

eth/protocols/eth/handler_test.go

@@ -424,7 +424,7 @@ func testGetBlockBodies(t *testing.T, protocol uint) {
 			RequestId:         123,
 			BlockBodiesPacket: bodies,
 		}); err != nil {
-			t.Errorf("test %d: bodies mismatch: %v", i, err)
+			t.Fatalf("test %d: bodies mismatch: %v", i, err)
 		}
 	}
 }