Fix Poly panel fix

[mikeskydev]

Checks for the panel existing before disabling. d'oh.

Sidenote, why doesn't m_NotSupportedMessage?.SetActive(false); work here?

[mikeage]

working! Thanks

[mikeage]

I'm going to merge this one, hope there are no objections

[TimAidley]

@mikeskydev, the reason m_NotSupportedMessage?.SetActive(false); doesn't work is that m_NotSupportedMessage points to a UnityEngine.Object-derived type, which means that it is a wrapper around a C++ object in the Unity Engine. As a result, C++ is in charge of its lifetime, rather than C#. Now, because C++ is in charge of lifetime, an object in C++ may get destroyed, while a reference to it still exists in C#.

To make this 'simpler', Unity set UnityEngine.Object so that if you test equality with null when the C++ object has been destroyed, it will return true. Most of the time this works fine, but it does mean that null coalescing operators don't work because a Unity object that we think of as null may actually not be null, but pointing to a destroyed object.

[mikeage]

That is a really helpful explanation, thank you!

[mikeskydev]

Yeah that explains a lot, thanks!