cartoon helix tubes choke on 1zik

[Elaine Meng]

Although I can show tube helices for several other models without this problem, it seems to barf up on PDB 1zik, stopping redraws:

open 1zik
car style modeh arc

cartoon style modeHelix arc
Error processing trigger "graphics update"
Traceback (most recent call last):
File "/Users/chimera/Applications/ChimeraX_Daily.app/Contents/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/chimerax/core/triggerset.py", line 126, in invoke
return self._func(self._name, data)
File "/Users/chimera/Applications/ChimeraX_Daily.app/Contents/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/chimerax/core/atomic/structure.py", line 1909, in _update_graphics_if_needed
s[i]._update_graphics_if_needed()
File "/Users/chimera/Applications/ChimeraX_Daily.app/Contents/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/chimerax/core/atomic/structure.py", line 269, in _update_graphics_if_needed
self._create_ribbon_graphics()
File "/Users/chimera/Applications/ChimeraX_Daily.app/Contents/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/chimerax/core/atomic/structure.py", line 782, in _create_ribbon_graphics
rp.vertices = concatenate(vertex_list)
ValueError: need at least one array to concatenate
Error in drawing scene. Redraw is now stopped.

... and then you can get the following many, many times ...

Traceback (most recent call last):
File "/Users/chimera/Applications/ChimeraX_Daily.app/Contents/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/chimerax/core/updateloop.py", line 43, in draw_new_frame
view.draw(check_for_changes = False)
File "/Users/chimera/Applications/ChimeraX_Daily.app/Contents/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/chimerax/core/graphics/view.py", line 179, in draw

self._update_projection(vnum, camera=camera)

File "/Users/chimera/Applications/ChimeraX_Daily.app/Contents/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/chimerax/core/graphics/view.py", line 735, in _update_projection
near, far = self.near_far_distances(c, view_num)
File "/Users/chimera/Applications/ChimeraX_Daily.app/Contents/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/chimerax/core/graphics/view.py", line 748, in near_far_distances
near, far = self._near_far_bounds(cp, vd)
File "/Users/chimera/Applications/ChimeraX_Daily.app/Contents/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/chimerax/core/graphics/view.py", line 761, in _near_far_bounds
b = self.drawing_bounds()
File "/Users/chimera/Applications/ChimeraX_Daily.app/Contents/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/chimerax/core/graphics/view.py", line 586, in drawing_bounds
dm.cached_drawing_bounds = b = self.drawing.bounds()
File "/Users/chimera/Applications/ChimeraX_Daily.app/Contents/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/chimerax/core/graphics/drawing.py", line 731, in bounds
dbounds = [d.bounds() for d in self.child_drawings() if d.display]
File "/Users/chimera/Applications/ChimeraX_Daily.app/Contents/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/chimerax/core/graphics/drawing.py", line 731, in <listcomp>
dbounds = [d.bounds() for d in self.child_drawings() if d.display]
File "/Users/chimera/Applications/ChimeraX_Daily.app/Contents/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/chimerax/core/atomic/structure.py", line 1329, in bounds
self._update_graphics_if_needed() # Ribbon bound computed from graphics
File "/Users/chimera/Applications/ChimeraX_Daily.app/Contents/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/chimerax/core/atomic/structure.py", line 269, in _update_graphics_if_needed
self._create_ribbon_graphics()
File "/Users/chimera/Applications/ChimeraX_Daily.app/Contents/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/chimerax/core/atomic/structure.py", line 782, in _create_ribbon_graphics
rp.vertices = concatenate(vertex_list)
ValueError: need at least one array to concatenate

[Conrad Huang]

Fixed in 11680f2.

In tube mode, 1zik only has tubes. The code was expecting some sort of ribbon to be displayed.