Merge pull request #3981 from RosettaCommons/roccomoretti/interactive_geom_validity
Foldit: Fix issue with puzzle switching and focus geometry.
When you have the camera focused on a residue at the end of the pose, and then switch to a puzzle with a smaller number of residues, you get a crash due to a lingering ResidueGeometry which references a now-nonexisting residue number.
To check for this, I added a Geometry::is_valid() function which can check for this case, and added a check in StandaloneCameraController to make sure that the geometry is valid before we switch.