hgview #3463 bug on empty repo [validation pending]

a traceback shows up when running hgview on an empty repo:

$ hgview
read_nodes 0.0 2.69412994385e-05
Computing graph...
START ['0000000000000000000000000000000000000000']
done in 0.0
Traceback (most recent call last):
  File "/home/bidule/SB/public/hgview/hgview.py", line 357, in idle_fill_model
    graph.build(NMAX)
  File "/home/bidule/SB/public/hgview/buildtree.py", line 141, in build
    self.rownlines[rowno] = len(todo)
IndexError: list assignment index out of range
prioritynormal
typebug
done in0.9.0
load1.000
load left0.000
closed by<not specified>