fix: handle case where contract is not verified

apps/block_scout_web/lib/block_scout_web/templates/transaction_log/index.html.eex

@@ -71,6 +71,8 @@
                         </tr>
                     <% end %>
                     </table>
+                  <% _ -> %>
+                    <%= nil %>
                 <% end %>
 
               </dd>

apps/explorer/lib/explorer/chain/log.ex

@@ -104,14 +104,14 @@ defmodule Explorer.Chain.Log do
   @doc """
   Decode transaction log data.
   """
-  def decode(log, transaction) do
-    abi = transaction.to_address.smart_contract.abi
-
+  def decode(log, %Transaction{to_address: nil}), do: {:error, :no_to_address}
+  def decode(log, %Transaction{to_address: %{smart_contract: %{abi: abi}}}) when not is_nil(abi) do
     with {:ok, selector, mapping} <- find_and_decode(abi, log),
          identifier <- Base.encode16(selector.method_id, case: :lower),
          text <- function_call(selector.function, mapping),
          do: {:ok, identifier, text, mapping}
   end
+  def decode(_log, _transaction), do: {:error, :contract_not_verified}
 
   defp find_and_decode(abi, log) do
     with {selector, mapping} <-