check if ets table exist

apps/explorer/lib/explorer/chain/block_number_cache.ex

@@ -13,15 +13,17 @@ defmodule Explorer.Chain.BlockNumberCache do
 
   @spec setup(Keyword.t()) :: :ok
   def setup(opts \\ []) do
+    if :ets.whereis(@tab) == :undefined do
       :ets.new(@tab, [
         :set,
         :named_table,
         :public,
         write_concurrency: true
       ])
+    end
 
-    update_cache()
     setup_opts(opts)
+    update_cache()
 
     :ok
   end