Fix IndexError in get_nth_subpath() and ensure it always returns a NumPy array (#4630)

* fix #3569 and #4629

* Add changes to opengl_vectorized_mobject.py

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Co-authored-by: Francisco Manríquez Novoa <49853152+chopan050@users.noreply.github.com>

Author: MqCreaple

manim/mobject/opengl/opengl_vectorized_mobject.py

@@ -1227,7 +1227,9 @@ def align_points(self, vmobject):
         def get_nth_subpath(path_list, n):
             if n >= len(path_list):
                 # Create a null path at the very end
-                return [path_list[-1][-1]] * nppc
+                if len(path_list) == 0:
+                    return np.tile(np.zeros(3), (nppc, 1))
+                return np.tile(path_list[-1][-1], (nppc, 1))
             path = path_list[n]
             # Check for useless points at the end of the path and remove them
             # https://github.com/ManimCommunity/manim/issues/1959

manim/mobject/types/vectorized_mobject.py

@@ -1785,7 +1785,9 @@ def align_points(self, vmobject: VMobject) -> Self:
         def get_nth_subpath(path_list, n):
             if n >= len(path_list):
                 # Create a null path at the very end
-                return [path_list[-1][-1]] * nppcc
+                if len(path_list) == 0:
+                    return np.tile(np.zeros(3), (nppcc, 1))
+                return np.tile(path_list[-1][-1], (nppcc, 1))
             path = path_list[n]
             # Check for useless points at the end of the path and remove them
             # https://github.com/ManimCommunity/manim/issues/1959