They are empty anyway when not needed, I think.

XLK is an extension for Excel backup file automatically created by
Excel upon opening of a document. The content is still a normal Excel
file so why not detect it correctly.

Error: Conditional jump or move depends on uninitialised value(s)
Fix: Ensure that nGroupShapeFlags is initialized in the constructor
Also cleaned up some duplicate variables

This temp-fixes formula imports and other problems
caused because of getCellBlock.

Use const reference in copy constructor if we are going to give it const objects.