Clear the last of the nil checks

Guards now cover the statements that follow them, and a couple of reads
are restructured so the narrowing survives.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

exp_util/module/module_exports.lua

@@ -551,7 +551,7 @@ function ExpUtil.move_items_to_surface(options)
             options.item = item
             entity = ExpUtil.get_storage_for_stack(options)
             entity.insert(options.item)
-            local item_stack = options.item --[[@as LuaItemStack]]
+            local item_stack = options.item --[[@as LuaItemStack]]
             item_stack.clear()
         end
     end
@@ -604,7 +604,7 @@ end
 --- @param n number
 --- @return string
 function ExpUtil.comma_value(n) -- credit http://richard.warburton.it
-    local left, num, right = string.match(n, "^([^%d]*%d)(%d*)(.-)$")
+    local left, num, right = string.match(n, "^([^%d]*%d)(%d*)(.-)$")
     assert(left and num and right)
     return left .. (num:reverse():gsub("(%d%d%d)", "%1, "):reverse()) .. right
 end