Fixes for E_NOTICE in mod/item.php (#5393)

Fixes for E_NOTICE in mod/item.php (#5393)

* Fixes applied:
- `if (is_array($some_array))` is better code style than `if ($some_array)` as
  the `if()` block really needs an array to be found
- same with `if ($some_id)`, maybe `if ($some_id > 0)` is a more proper check
- added missing field 'emailcc' to Item::ITEM_FIELDLIST

Signed-off-by: Roland Häder <roland@mxchange.org>
* Fixes E_NOTICE of missing variable (PHP's lazyness again).

Signed-off-by: Roland Häder <roland@mxchange.org>
* Use !empty() to avoid accessing empty array.

Signed-off-by: Roland Häder <roland@mxchange.org>