Golden Layout can break if a panel throws while dragging

[mofojed]

Description

Discovered while investigating deephaven/deephaven-plugins#40, the entire layout breaks when a panel throws while dragging. Add some safeguards to prevent one erroneous panel from breaking the entire layout.

Steps to reproduce

1. Follow the steps in Plotly - multiple series plots with color axis cause error when trying to move panel deephaven-plugins#40

Expected results

1. Panel should drop correctly, layout shouldn't be broken (though that particular panel may be displaying incorrectly)

Actual results

1. Layout breaks, panel can't drop

Additional details and attachments