fix single-line correction

Author: hiaselhans

openglider/lines/knots.py

@@ -104,7 +104,7 @@ def get(self, lower_type: LineType, upper_type: LineType, upper_num: int) -> lis
                 raise Exception(f"whooot {lower_type} and {upper_type} with {upper_num} top")
 
         if upper_num == 1:
-            return [first]
+            return [first*0.001]
 
         values = [(first + index * (last-first) / (upper_num-1)) * 0.001 for index in range(upper_num)]
         x=1