obj: ignore polyline

obj.py

@@ -113,6 +113,7 @@ def parse_face(line):
 def parse_object_event(line):
     assert len(line) == 1
     name, = line
+    name = name.replace(".", "_").replace("-", "_")
     return ObjectEvent(name)
 
 def parse_usemtl(line):
@@ -141,6 +142,9 @@ def parse_line(line):
     if t == 's':
         # smooth shading
         return None
+    if t == 'l':
+        # polyline
+        return None
     assert False, (t, line)
 
 def parse_obj_lines(lines):