A drop indicator doesn't appear when dropping a question between two custom widgets

[JaneSjs]

T20549 - Placement Indicator is not appearing in surveyjs Editor when adding the custom question through drag and drop.
https://surveyjs.answerdesk.io/internal/ticket/details/T20549

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To reproduce the issue, run this demo and try to drop a question between two custom widgets. A drop indicator does not appear.