Display Nonexistent Evidence Crashes Player

[Enthalpy]

Trying to display a nonexistent piece of evidence hangs the editor. This isn't a browser issue, but a problem in the JavaScript itself.

Instead, the browser should simply ignore the request to display the evidence.

This problem likely occurs for other actions where fields expect a value, but doesn't have one.

[Enthalpy]

May be related: Finding that expressions like f:evidence_is_revealed('preuve', 1) hang the editor if piece of evidence 1 does not exist.

Initial report did not specify if this was in a particular action, or all actions.