bug fix osx: screeninfo: don't plan on testing OSX or other environments...

bug fix osx: screeninfo: don't plan on testing OSX or other environments myself. For this reason, I strongly encourage pull requests.

flatland/utils/graphics_pil.py

 import io
 import os
+import platform
 import time
 import tkinter as tk
 
@@ -45,9 +46,14 @@ class PILGL(GraphicsLayer):
         if jupyter is False:
             self.screen_width = 99999
             self.screen_height = 99999
-            for m in get_monitors():
-                self.screen_height = min(self.screen_height, m.height)
-                self.screen_width = min(self.screen_width, m.width)
+
+            if platform.system() == "Windows" or platform.system() == "Linux":
+                for m in get_monitors():
+                    self.screen_height = min(self.screen_height, m.height)
+                    self.screen_width = min(self.screen_width, m.width)
+            else:
+                self.screen_width = 800
+                self.screen_height = 600
 
             w = (self.screen_width - self.width - 10) / (self.width + 1 + self.linewidth)
             h = (self.screen_height - self.height - 10) / (self.height + 1 + self.linewidth)