Fix EXPBAS

There was an indexing error in Expbas. This MR contains a fix and a test for it.

Full credit goes to @coen.degraaf who found the bug and suggested the fix.

While fixing this bug I also commited a slight change to the gridit.py tool.

• Documentation updated or not needed.
• Test created or not needed.
• Attribution in source files and CONTRIBUTORS.md updated if necessary.