Folding code after opening new view into file crashes app.

[ghost]

Test:

• Open any file.
• Open a new view into the file (Menubar / File / New View into File).
• Fold any code.
• Mac OS X alert dialog pops up: "plugin_host has exited unexpectedly, plugin functionality won't be available until Sublime Text has been restarted"
• Keyboard shortcuts and code linting are now broken.
• Remove CursorRuler package. Issue resolves.
• Reinstall package. Issue returns.

Environment:

• Mac OS El Capitan 10.11.6 (15G1004)
• Sublime Text 3 Build 3126