[ENH] Trackers, Mathematical field : Better verbose on error when the parameter calculation is empty or filled with whitespace

Fixed the issue with the mathematical tracking field when the calculation parameter is empty when saving the item by customizing the error message for administrators and for users who have permission to edit the tracker (tiki_p_admin_trackers). Related merge request !1378 (closed)

Before : Expecting "(" near ""

After : The field option, Calculation is empty.

Tickets :

• Avan.tech : https://avan.tech/item74141
• dev.tiki.org : https://dev.tiki.org/item8071