Fix internal server error when using spreadsheet from a saved seach with a custom column layout

An internal server error message is displayed when using spreadsheet from a saved search which has a custom column layout.

See comments.

Step to reproduce:

• go to search tab
• switch to list view
• edit the column layout (add all the available columns)
• save the search ("save as button")
• refresh (select the default search in the drop down list and then select the saved one again)
• open spreadsheet