paralel edges - check fails

[Dealga McArdle]

thanks to lijenstina on irc freenode blenderpython for pointing it out.

Traceback (most recent call last):
  File "C:\Users\zeffi\Desktop\scripts\addons_contrib\mesh_tinyCAD\VTX.py", line 148, in execute
    if checkVTX(self, context):
  File "C:\Users\zeffi\Desktop\scripts\addons_contrib\mesh_tinyCAD\VTX.py", line 59, in checkVTX
    getVTX(self)
  File "C:\Users\zeffi\Desktop\scripts\addons_contrib\mesh_tinyCAD\VTX.py", line 15, in getVTX
    self.point = cm.get_intersection(self.edge1, self.edge2)
  File "C:\Users\zeffi\Desktop\scripts\addons_contrib\mesh_tinyCAD\cad_module.py", line 41, in get_intersection
    return ((line[0] + line[1]) / 2)
TypeError: 'NoneType' object is not subscriptable

intersect_line_line : Takes 2 segments (defined by 4 vectors) and returns a vector for their point of intersection or None.

in the case of non intersecting lines this should return None, hence the error.

[Dealga McArdle]

i've added code to prevent this from happening. Thinks it's resolved now, but more testing is always welcome.