PyOpenGL exception when exiting in nogui mode

[Greg Couch]

Exception ignored in: <bound method Framebuffer.__del__ of <chimera.core.graphics.opengl.Framebuffer object at 0x7f63a758ba90>>
Traceback (most recent call last):
  File "/home/gregc/src/chimera2/Chimera2.app/lib/python3.5/site-packages/chimera/core/graphics/opengl.py", line 925, in __del__
  File "/home/gregc/src/chimera2/Chimera2.app/lib/python3.5/site-packages/chimera/core/graphics/opengl.py", line 1011, in delete
  File "latebind.pyx", line 44, in OpenGL_accelerate.latebind.Curry.__call__ (src/latebind.c:1201)
  File "/home/gregc/src/chimera2/Chimera2.app/lib/python3.5/site-packages/PyOpenGL-3.1.0-py3.5.egg/OpenGL/GL/ARB/framebuffer_object.py", line 328, in glDeleteFramebuffers
  File "latebind.pyx", line 32, in OpenGL_accelerate.latebind.LateBind.__call__ (src/latebind.c:989)
  File "wrapper.pyx", line 299, in OpenGL_accelerate.wrapper.Wrapper.__call__ (src/wrapper.c:6294)
  File "wrapper.pyx", line 161, in OpenGL_accelerate.wrapper.PyArgCalculator.c_call (src/wrapper.c:4241)
  File "wrapper.pyx", line 128, in OpenGL_accelerate.wrapper.PyArgCalculatorElement.c_call (src/wrapper.c:3601)
  File "wrapper.pyx", line 114, in OpenGL_accelerate.wrapper.PyArgCalculatorElement.c_call (src/wrapper.c:3409)
  File "wrapper.pyx", line 212, in OpenGL_accelerate.wrapper.CallFuncPyConverter.c_call (src/wrapper.c:5103)
  File "arraydatatype.pyx", line 174, in OpenGL_accelerate.arraydatatype.ArrayDatatype.asArray (src/arraydatatype.c:4221)
  File "arraydatatype.pyx", line 49, in OpenGL_accelerate.arraydatatype.HandlerRegistry.c_lookup (src/arraydatatype.c:2061)
  File "/home/gregc/src/chimera2/Chimera2.app/lib/python3.5/site-packages/PyOpenGL-3.1.0-py3.5.egg/OpenGL/plugins.py", line 16, in load
  File "/home/gregc/src/chimera2/Chimera2.app/lib/python3.5/site-packages/PyOpenGL-3.1.0-py3.5.egg/OpenGL/plugins.py", line 38, in importByName
  File "<frozen importlib._bootstrap>", line 969, in _find_and_load
  File "<frozen importlib._bootstrap>", line 954, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 887, in _find_spec
TypeError: ("'NoneType' object is not iterable", None)

[Tom Goddard]

Fixed.

Code was trying to delete the default framebuffer (0) when exiting.