fix double mining sounds for resources

scripts/mining-tools.lua

@@ -7,10 +7,10 @@ function mod.play_mining_sound(pindex)
    --game.print("1",{volume_modifier=0})--
    if player and player.mining_state.mining and player.selected and player.selected.valid then
       --game.print("2",{volume_modifier=0})--
-      if player.selected.prototype.is_building then
+      if player.selected and player.selected.prototype.is_building then
          player.play_sound({ path = "player-mine" })
          --game.print("3A",{volume_modifier=0})--
-      else
+      elseif player.selected and player.selected.type ~= "resource" then
          player.play_sound({ path = "player-mine" }) --Mine other things, eg. character corpses, laterdo new sound
          --game.print("3B",{volume_modifier=0})--
       end