Fix Line failing with buff and path_arc (#4132)

Author: irvanalhaq9

manim/mobject/types/vectorized_mobject.py

@@ -1938,24 +1938,27 @@ def pointwise_become_partial(
                 upper_residue,
             )
         else:
+            # make a copy of points before setting self.points = np.empty(...)
+            vmobject_points = vmobject.points.copy()
+            
             # Allocate space for (upper_index-lower_index+1) Bézier curves.
             self.points = np.empty((nppc * (upper_index - lower_index + 1), self.dim))
             # Look at the "lower_index"-th Bezier curve and select its part from
             # t=lower_residue to t=1. This is the first curve in self.points.
             self.points[:nppc] = partial_bezier_points(
-                vmobject.points[nppc * lower_index : nppc * (lower_index + 1)],
+                vmobject_points[nppc * lower_index : nppc * (lower_index + 1)],
                 lower_residue,
                 1,
             )
             # If there are more curves between the "lower_index"-th and the
             # "upper_index"-th Béziers, add them all to self.points.
-            self.points[nppc:-nppc] = vmobject.points[
+            self.points[nppc:-nppc] = vmobject_points[
                 nppc * (lower_index + 1) : nppc * upper_index
             ]
             # Look at the "upper_index"-th Bézier curve and select its part from
             # t=0 to t=upper_residue. This is the last curve in self.points.
             self.points[-nppc:] = partial_bezier_points(
-                vmobject.points[nppc * upper_index : nppc * (upper_index + 1)],
+                vmobject_points[nppc * upper_index : nppc * (upper_index + 1)],
                 0,
                 upper_residue,
             )