Moved from ZBX-16432 subissue #5

Steps to reproduce:

• Create a host with a single item.
• Export host (XML file).
• Delete the host
• Delete a value from item <name> field from XML.
• Import it back. ( import file zbx_export_empty_item_name.xml )

Result: Host and item are successfully imported. Item has an empty name and there is no option to open the edit screen.

Note: the same issue appears if discovery_rule and item_prototype name is empty e.g. import file discovery_rule_and_item_prototype_test_import.xml
On master, validation is missing only if the discovery_rule name is empty.

Expected: An error should appear during importing process.