Exit from an update item modal in the plugin List goes to undefined page instead of staying in the page

• Regression

After clicking on the save button on a modal the user is redirected to the page "undefined".
This happen since Tiki21 and it is working fine in Tiki20.

Tested on : tiki-21.0.RC1

To reproduce:

1. Login as Admin
2. Enable trackers and button plugin
3. Create a tracker with a few fields (in the fade I pasted the export for the tracker and the fields)
   
   Tracker export

   TRACKER
   adminOnlyViewEditItem = n
   autoAssignCreatorGroup = n
   autoAssignCreatorGroupDefault = n
   autoAssignGroupItem = n
   autoCopyGroup = n
   autoCreateCategories = n
   autoCreateGroup = n
   defaultOrderDir = asc
   defaultOrderKey = -1
   defaultStatus = o
   doNotShowEmptyField = n
   fieldPrefix = contact
   newItemStatus = o
   oneUserItem = n
   orderAttachments = created,hits,filesize
   publishRSS = n
   ratingOptions = -2,-1,0,1,2
   saveAndComment = n
   sectionFormat = flat
   showAttachments = n
   showComments = n
   showCreated = n
   showCreatedBy = n
   showCreatedView = n
   showLastComment = n
   showLastModif = n
   showLastModifBy = n
   showLastModifView = n
   showRatings = n
   showStatus = n
   showStatusAdminOnly = n
   simpleEmail = n
   useAttachments = n
   useComments = n
   useFormClasses = n
   useRatings = n
   userCanSeeOwn = n
   userCanTakeOwnership = n
   writerCanModify = n
   writerCanRemove = n
   writerGroupCanModify = n
   writerGroupCanRemove = n
   trackerId = 1
   name = Contact
   descriptionIsParsed = n
   created = 1584087369
   lastModif = 1584087369

   
   
   Field Export

   FIELD1
   fieldId = 1
   name = Name
   permName = contactName
   position = 10
   type = t
   options =
   isMain = y
   isTblVisible = y
   isSearchable = n
   isPublic = y
   isHidden = n
   isMandatory = y
   description =
   descriptionIsParsed = n
   FIELD2
   fieldId = 2
   name = Country
   permName = contactCountry
   position = 20
   type = y
   options =
   isMain = n
   isTblVisible = n
   isSearchable = n
   isPublic = y
   isHidden = n
   isMandatory = n
   description =
   descriptionIsParsed = n
   FIELD3
   fieldId = 3
   name = Date
   permName = contactDate
   position = 30
   type = j
   options =
   isMain = n
   isTblVisible = n
   isSearchable = n
   isPublic = y
   isHidden = n
   isMandatory = n
   description =
   descriptionIsParsed = n
   FIELD4
   fieldId = 4
   name = Image
   permName = contactImage
   position = 40
   type = FG
   options = {"galleryId":0,"filter":"","count":0,"displayMode":"","displayParams":"","displayParamsForLists":"","displayOrder":"","deepGallerySearch":0,"replace":"n","browseGalleryId":0,"duplicateGalleryId":0,"indexGeometry":"","uploadInModal":"y","image_x":"","image_y":"","addDecriptionOnUpload":"n","requireTitle":"n"}
   isMain = n
   isTblVisible = n
   isSearchable = n
   isPublic = y
   isHidden = n
   isMandatory = n
   description =
   descriptionIsParsed = n

4. Populate the tracker with a few items
5. Edit a page and create a pluginList with an edit button
   In my sample I used a table output with fixed values for editing the item 1 only (pasted below)
   I tested with a link and a button to be sure
   
   PluginList content

   No results for query.

Your page should end with something like this:

When you click on the link or the button you will have the "Update Item" modal.

• Close will bring back to the page (GOOD)
• Preview won’t do nothing (I think it shouldn’t be here don’t see how it will be used)
• Save will save but redirect the user to an "undefined" page (BROKEN)
  
  Video : https://share.vidyard.com/watch/UCAew92XGPH4zHUQ3G2QbG?

Saving used to redirect to the page, same list, same result (if customSearch) in Tiki20.
Here a Tiki20 (using smarty template) with the same code for the button:
https://share.vidyard.com/watch/w8zwARp8C3X1aB4xFSiyma?

This bug has been demonstrated on show2.tiki.org

Please demonstrate your bug on show2.tiki.org