gc reference before construction when running chaco.chaco.plots.polar_line_renderer.py

[homosapien-lcy]

in chaco.chaco.plots.polar_line_renderer, in function _draw_plot(). Function will try to call _render on gc (line 136), which is a parameter not exists. Need to find someway to add the construction of gc

[dpinte]

Opened PR here: #883