Fix #833 by adding correct number of edges

The mesh structure was invalid because the vertex indices for only one edge were set. The other edge had the same index for both vertices.

src/ifcblenderexport/blenderbim/bim/annotation.py

@@ -62,7 +62,7 @@ class Annotator:
             obj.data.vertices.add(2)
             obj.data.vertices[-2].co = co1
             obj.data.vertices[-1].co = co2
-            obj.data.edges.add(2)
+            obj.data.edges.add(1)
             obj.data.edges[-1].vertices = (obj.data.vertices[-2].index, obj.data.vertices[-1].index)
         if isinstance(obj.data, bpy.types.Curve):
             polyline = obj.data.splines.new('POLY')