Merging step fails for some tiles across nodes

[julietcohen]

During the merge step, executed with merge_staged_vector_tiles.py, most tiles in worker nodes succeed in undergoing one of the following:

1. being copied over to the head node (if the tile does not yet exist in the head node at all)
2. being merged (deduplicated) into the tile that already exists in the head node (because the tile existed in both nodes, but the files are different)
3. being skipped, so nothing is done (because the tile exists in both nodes, and the files are the same)

Some errors occur when merging:

The errors imply that either one of the matching tiles is corrupted in general, or that more specifically the geometry at index 0 is invalid due to a self-intersection.