[dagit] Fix mode-less pipeline paths

Summary: There is an infinite loop when loading a pipeline URL that does not have a mode. Repair this by being more restrictive about our effect dependencies.

Test Plan: Load http://localhost:3000/workspace/toys_repository@dagster_test.toys.repo/pipelines/asset_lineage_pipeline, verify redirect to :default and no infinite loops.

Reviewers: bengotow

Reviewed By: bengotow

Differential Revision: https://dagster.phacility.com/D8247