fix: handle products without positions obj

[aldeed]

Resolves #4299
Impact: minor
Type: bugfix

Issue

If any documents in Catalog collection do not have a positions property, migration fails on startup on first start after migration to v1.12.0. The migration is left locked. The error message is:

0|reaction | TypeError: Cannot convert undefined or null to object
0|reaction |     at Function.keys (<anonymous>)
0|reaction |     at items.forEach (imports/plugins/core/versions/server/migrations/25_update_catalog_schema.js:28:12)

Solution

Handle undefined positions prop in the migration.

Breaking changes

NONE

Testing

1. Start Reaction with v1.11.0 and load data.
2. In Mongo, make sure at least one document in Catalog collection has no positions property.
3. Upgrade code to v1.12.0
4. Start Reaction and make sure all migrations run without issue, and the app runs properly afterward.

[spencern]

@zenweasel once you've confirmed this fix, we'll push this out as 1.12.1

[brent-hoover]

Tested. Verified fixed