Some performance fixes
Created originally on Bitbucket by Blackeagle52 (Peter Pul)
Changesets for this Pull Request have not been imported, because it had been already declined on Bitbucket. Marked as closed by the import user.
- Removed if topLeftCell is not None, as it is obsolute with the if before
- Worksheet has no self._hyperlinks
- Added top left cell check, and replaced min_row/max_row/min_col/max_col check with using calculate dimension, loops only once over all cells, instead of two times, with very large files.
- Removed calling the min_row and max_row properties within columns, with very expensive with very large Excel files