fix(canvas): restore first-vertex snap highlight when closing polygon

highlightClear() ran after self.update(), so the async paint event fired
after the highlight had already been cleared. Clear at the top of the
draw branch instead so the NEAR_VERTEX highlight set by the snap check
is still present when the paint event runs.

Author: wkentaro

labelme/widgets/canvas.py

@@ -385,6 +385,7 @@ def mouseMoveEvent(self, a0: QtGui.QMouseEvent) -> None:
                 self._update_status()
                 return
 
+            self.current.highlightClear()
             if self.outOfPixmap(pos):
                 # Don't allow the user to draw outside the pixmap.
                 # Project the point to the pixmap's edges.
@@ -433,7 +434,6 @@ def mouseMoveEvent(self, a0: QtGui.QMouseEvent) -> None:
                 self.line.close()
             assert len(self.line.points) == len(self.line.point_labels)
             self.update()
-            self.current.highlightClear()
             self._update_status()
             return