Crash in moonray_gui when using camera controls

[jlanz]

If you navigate the scene in moonray_gui_v2 or moonray_gui v1 using the camera controls, it sometimes triggers this segfault:

SIGFPE(float point exception) callstack
librendering_mcrt_common.so(_ZN7moonray11mcrt_common19debugPrintCallstackEPKc+0x72) [0x7ff0e50c1612]
 libapplication.so(_ZN7moonray17stackTraceHandlerEi+0x5c) [0x7ff0f223f22c]
  libc.so.6(+0x3e730) [0x7ff0dd03e730]
   librendering_rndr.so(_ZN7moonray4rndr18populateLightStatsERSt6vectorINS0_9LightStatESaIS2_EERfS6_S6_S6_RKNS_3pbr10StatisticsEPKNS7_5SceneERKN10scene_rdl24rdl214SceneVariablesE+0x276) [0x7ff0f21443d6]
    librendering_rndr.so(_ZN7moonray4rndr11RenderStats13logLightStatsERKNS_3pbr10StatisticsEPKNS2_5SceneERKN10scene_rdl24rdl214SceneVariablesE+0xf8) [0x7ff0f2158198]
     librendering_rndr.so(_ZN7moonray4rndr13RenderContext9stopFrameEb+0xab0) [0x7ff0f2043220]
      moonray_gui() [0x4594e7]
       moonray_gui() [0x42fd95]
        libc.so.6(+0x897fa) [0x7ff0dd0897fa]