Avoid division by 0 in perimeter_of_ellipse calculation

While the initial cause of the division by 0 error mentioned in #44
should be fixed, now that this function will never be passed negative
numbers, it's still possible when both rx and ry are 0.

Add a special case to handle either rx or ry being 0, which returns
the "perimeter" of the ellipse as being the twice the length of the
line segment between the extremeties. (If both rx or ry are 0, the
resulting perimeter will be 0.)

bbb_presentation_video/renderer/tldraw/utils.py

@@ -181,6 +181,13 @@ class Decoration(Enum):
 
 def perimeter_of_ellipse(rx: float, ry: float) -> float:
     """Find the approximate perimeter of an ellipse."""
+
+    # Handle degenerate case where the "ellipse" is actually a line or a point
+    if rx == 0:
+        return 2 * ry
+    elif ry == 0:
+        return 2 * rx
+
     h = (rx - ry) ** 2 / (rx + ry) ** 2
     return pi * (rx + ry) * (1 + (3 * h) / (10 + sqrt(4 - 3 * h)))