Reset the camera's view angle in vtkRenderer::ResetCamera.

Otherwise zooming and resetting the camera repeatedly will cause the
view angle to approach 0, eventually leading to odd z-buffer artifacts.

Change-Id: Icbb486d94c44f3761f0e9afdff1695deeea0b1b9
Merge topic 'screwy-zbuffer' into master

a86227da Reset the camera's view angle in vtkRenderer::ResetCamera.