fix(fonttools): stop the contour walk at the closing point

When an off-curve run ended on first_on, the walk set cur=first_on and
wrapped past it, repeating the contour and overflowing the edge table.
Break immediately after drawing the closing quadratic.

vpsdk/fonttools/fonttools.vp

@@ -240,6 +240,7 @@ def _build_contour(start: int, end: int):
                 cx = _px[nn]
                 cy = _py[nn]
                 cur = nn
+                if nn == first_on: break
             else:
                 mx: float = (_px[ctrl] + _px[nn]) / 2.0
                 my: float = (_py[ctrl] + _py[nn]) / 2.0