Viewer crashes when 'view springs' is checked but no springs are present

[Robert Welch]

The viewer should continue loading, ignoring the springs. The ‘draw springs’ option is enabled by default and the crash message doesn’t give the user much info wrt springs.

This doesn’t happen on my branch (rods), but I assume it’s on superdev. I’m guessing it’s not on stable, but I don’t know if there haven been any updates to stable recently.

Attached are some files courtesy of Ryan, who found this bug - a log and simulation files that can reproduce it.

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