[Lang] Fix fractal gui close warning (#5281)

* fix fractal gui close warning

* fix fractal gui close warning

Author: neozhaoliang

python/taichi/examples/simulation/fractal.py

@@ -25,9 +25,10 @@ def paint(t: float):
 
 def main():
     gui = ti.GUI("Julia Set", res=(n * 2, n))
-
-    for i in range(1000000):
-        paint(i * 0.03)
+    t = 0.0
+    while not gui.get_event(ti.GUI.ESCAPE, ti.GUI.EXIT):
+        paint(t)
+        t += 0.03
         gui.set_image(pixels)
         gui.show()