Adding pseudobonds causes graphics error

[Greg Couch]

Finding hydrogen bonds for 1eyg produces:

414 hydrogen bonds found
Error processing trigger "graphics update"
Traceback (most recent call last):
File "/Users/pett/src/chimerax/ChimeraX.app/Contents/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/chimerax/core/triggerset.py", line 126, in invoke
return self._func(self._name, data)
File "/Users/pett/src/chimerax/ChimeraX.app/Contents/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/chimerax/core/atomic/structure.py", line 2230, in _update_graphics_if_needed
s[i]._update_graphics_if_needed()
File "/Users/pett/src/chimerax/ChimeraX.app/Contents/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/chimerax/core/atomic/structure.py", line 309, in _update_graphics_if_needed
self._update_graphics(gc)
File "/Users/pett/src/chimerax/ChimeraX.app/Contents/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/chimerax/core/atomic/structure.py", line 327, in _update_graphics
pbg._update_graphics(changes)
File "/Users/pett/src/chimerax/ChimeraX.app/Contents/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/chimerax/core/atomic/pbgroup.py", line 143, in _update_graphics
d.positions = self._update_positions(pbonds, bond_atoms)
File "/Users/pett/src/chimerax/ChimeraX.app/Contents/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/chimerax/core/atomic/pbgroup.py", line 160, in _update_positions
return s._halfbond_cylinder_placements(axyz0, axyz1, pbonds.radii)
File "/Users/pett/src/chimerax/ChimeraX.app/Contents/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/chimerax/core/atomic/structure.py", line 2593, in _halfbond_cylinder_placements
half_cylinder_rotations(axyz0, axyz1, radii, p)
ValueError: Cylinder end-point and radii arrays must have same size, got 2 and 2

[Eric Pettersen]

Fixed the hbonds command throwing an error with no structures open, leaving what seems to be a new bug in the graphics-drawing code, so changed the summary and description and re-assigned to T.G.