Malformed transition routing breaks visualization

[Phrogz]

1. Open/create a working diagram
2. Hand-edit a viz:pts attribute for a transition to have an incorrect format like viz:pts="S X100" or viz:pts="X100 Y X200"

EXPECTED: The transition path ignores the malformed attachment point, or does something clever like infers a 0 value. Should also show a warning or error in the Problems panel.
ACTUAL: All states and some transitions stop drawing as a runtime error is experienced.