Fixed a crash on importing named ranges on higher sheets.
Fixed a crash on importing named ranges on higher sheets.

When importing xls document containing named ranges on sheets higher
than 256 (max number of sheets Calc supports currently), Calc would
crash.  We need to check for the upper boundary condition before
accessing the array by index to prevent crash. (n#649941)

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core