SELECT 
  * 
FROM 
  cscart_bm_locations as l 
  LEFT JOIN cscart_bm_locations_descriptions as d ON d.location_id = l.location_id 
  AND d.lang_code = 'en' 
WHERE 
  l.layout_id = 2 
  AND l.dispatch IN ('categories.view') 
  AND (
    FIND_IN_SET(271, l.object_ids) 
    OR l.object_ids = ''
  ) 
ORDER BY 
  l.object_ids desc 
LIMIT 
  1

Query time 0.00031

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "read_sorted_file": {
          "filesort": {
            "sort_key": "l.object_ids desc",
            "table": {
              "table_name": "l",
              "access_type": "ALL",
              "rows": 30,
              "filtered": 100,
              "attached_condition": "l.layout_id = 2 and l.dispatch = 'categories.view' and (find_in_set(271,l.object_ids) or l.object_ids = '')"
            }
          }
        }
      },
      {
        "table": {
          "table_name": "d",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "10",
          "used_key_parts": ["location_id", "lang_code"],
          "ref": ["u358358020_main.l.location_id", "const"],
          "rows": 1,
          "filtered": 100,
          "attached_condition": "trigcond(d.location_id = l.location_id and d.lang_code = 'en')"
        }
      }
    ]
  }
}