grids.BingTileGridGenerator.generate_grid_join crashing when running with zoom 18

[janzkyle]

In 01_aoi_grids_zoom18.ipynb, changing the zoom level from 16 to 18 crashes after running the generate_grid_join() for around 30 mins

Error log:

Cannot execute code, session has been disposed. Please try restarting the Kernel.
The Kernel crashed while executing code in the the current cell or a previous cell. Please review the code in the cell(s) to identify a possible cause of the failure. Click [here](https://aka.ms/vscodeJupyterKernelCrash) for more info. View Jupyter [log](command:jupyter.viewOutput) for further details.