Bezier curves are acting erratically with high pitch levels

[k-stf]

maptalks's version and what browser you use?

1.0.0.rc37, Chrome/Firefox

Issue description

Bezier curves are acting erratically when pitch/zoom combination is high enough (higher the pitch, lower zoom level is required to trigger the problem). When you move the map, Bezier curves are moving/flickering/turning to straight lines.

Please provide a reproduction URL (on any jsfiddle like site)

https://jsfiddle.net/3nreykjh/
Try moving map forward and backward, you will see bezier curve turning into straight line when approximately half of the line is out of the screen.

[k-stf]

same problem with all curves. looks like this happens when one of the points is out of viewport (most probably the problem is in _projIfBehindCamera)