Latest update reduces error-tolerance for missing images in image nodes

[GoogleCodeExporter]

Create a dot format with some image nodes, calling, say GOODIMAGE and one
for BADIMAGE, and make sure the bad image does not exist.

Running it through graphviz gives a warning:
Warning: BADIMAGE was not found as a file or as a shape library member
Warning: No or improper image=BADIMAGE for node "node2"

The output will be along the lines of (one good node and one bad):
node49 [label="", image=GOODIMAGE, width="1.31", height="0.61",
pos="128,983", _draw_="I 81 962 94 42 6 -Purina "];
node50 [label="", image=BADIMAGE, width="0.25", height="0.25", pos="450,750"];

Previously Canviz drew the graph and simply left a blank spot for the
missing image.  Now it bails on an "Undefined value" error at canviz.js
line 450:
draw_attr_hash = containers[0].drawAttrs;

Since there are no _draw_ commands for the latter, this is where canviz is
getting bogged down.  I'm not sure how deep the architecture changes have
been in the last week, but it has increased the sensitivity too much.

Original issue reported on code.google.com by omn...@gmail.com on 2 Nov 2008 at 6:04

[GoogleCodeExporter]

Thanks for the report! There have been a lot of changes recently and I'm glad 
someone else is testing them out.

Could you please attach here (or, if confidential, email me) a dot file that 
causes this error? Entities with no 
_*draw_ commands don't appear to be the problem; it least, they don't cause an 
error for me, using Canviz from 
r209.

Original comment by ryandesi...@gmail.com on 2 Nov 2008 at 8:27