Camera switching sometimes crashes

[jspjutNV]

Since #118 added the ability to use different cameras, and particularly the debug camera to look around the scene, I noticed a bug where switching from some additional cameras back to the player camera or debug camera occasionally causes FPSci to crash.

We need to more carefully figure out how to reproduce this bug on the way to fixing it.

[bboudaoud-nv]

I suggest deferring this issue, as using non-primary cameras is not a standard feature for FPSci users or developers. Also this issue seems to occur infrequently enough that it is difficult to produce a minimum and precise reproducible example for.

[jspjutNV]

Using non-primary cameras is a standard feature of G3D applications so we have a regression compared to G3D. I'm fine pushing this to later, but I think it should stay on our list of things we'll fix.

That said, this bug is also relatively minor since it only crashes sometimes, so I don't mind having us take a while to fix it.