Map variable nodes don't show field errors anywhere in node edit popup

[raphaelsolarski]

Describe the bug A clear and concise description of what the bug is

To Reproduce

1. Create map variable
2. Provoke error in one filed e.g. put invalid spell expression like '

Environment (please fill in the following information):

• Nussknacker version 1.8.1

[bartektartanus]

The error is shown, when field name is empty, but it is located at the top.