Position attribute possibly wrong (0-indexed) for remote ingests

[blms]

We noticed in a meeting that some position attributes start at 0 for canvases, possibly due to remote ingest issues.

Example on dev with 0 index:
https://dev.readux.io/iiif/v2/2qnsf0jr/manifest

Example on dev with 1 index:
https://dev.readux.io/iiif/v2/1898-Fillm2-EMU/manifest

Note that canvas label is serialized from Canvas.position:

readux/apps/iiif/serializers/canvas.py

Line 20 in 6d03b12

obj.label = str(obj.position)