Drawing a polygon with one edge along the south pole returns error

Hi,

this code:

import tkinter as tk  
import tkintermapview  
  
  
root = tk.Tk()  
map = tkintermapview.TkinterMapView(root, height=1000, width=1000)  
polygon = map.set_polygon([(-35.0, -10.0), (-35.0, 15.0), (-90.0, 15.0), (-90.0, -10.0), (-35.0, -10.0)])  
  
map.pack()  
root.mainloop()

returns this error:

Traceback (most recent call last):
  File "Z:/OverpassBBoxStitcher/test.py", line 7, in <module>
    polygon = map.set_polygon([(-35.0, -10.0), (-35.0, 15.0), (-90.0, 15.0), (-90.0, -10.0), (-35.0, -10.0)])
  File "Python36\site-packages\tkintermapview\map_widget.py", line 381, in set_polygon
    polygon.draw()
  File "Python36\site-packages\tkintermapview\canvas_polygon.py", line 101, in draw
    canvas_position = self.get_canvas_pos(position, widget_tile_width, widget_tile_height)
  File "Python36\site-packages\tkintermapview\canvas_polygon.py", line 74, in get_canvas_pos
    tile_position = decimal_to_osm(*position, round(self.map_widget.zoom))
  File "Python36\site-packages\tkintermapview\utility_functions.py", line 12, in decimal_to_osm
    ytile = (1.0 - math.log(math.tan(lat_rad) + (1 / math.cos(lat_rad))) / math.pi) / 2.0 * n
ValueError: math domain error

I will work around this issue by clamping all the south values to -89.99999, but that feels hacky and un-elegant.
For the north pole, a similar issue does not occur.

This is what I want it to look like:

Reproduce the example in canvas_polygon.py and follow its call into utility_functions.py, where decimal_to_osm raises the math domain error for latitude -90. Check how map_widget.py invokes polygon.draw(). Done means the supplied polygon can be drawn along the south pole without the exception, with the existing north-pole behavior preserved.