Fix lookup for columns that are multiples of 26

This fixes an issue where spreadsheets that use aliases on columns greater than 51 get an error: "The element at position 0 cannot be found. "

This happens because the code to determine the 2nd character of the column reference (AA, AB, etc.) uses the mod operator. If the celI index is a multiple of 26, modulus returns 0 resulting in an error referencing the ColumnLookup array.

This change adds an IIF statement to return the length of the array (26) instead of the result of the modulus if that result is 0.