fix(desk): Use key matching label if key with fieldname doesn't exist

[adityahase]

For example for Item Variant Details with following data

Report exported as Excel doesn't include data for some of the columns

Before

After

[sagarvora]

The parentheses in your PR title must match the affected module (e.g. accounts).

[adityahase]

The parentheses in your PR title must match the affected module (e.g. accounts).

This fixes "reports", Item Variant Details is just an example.

[sagarvora]

This fixes "reports", Item Variant Details is just an example.

The module is desk.