fix webtrader bug
fix webtrader bug

1.fix issue#763
2.fix issue#753
3.fix issue#741
harveywwu/vnpy,msincenselee/vnpy,andrewchenshx/vnpy,andrewchenshx/vnpy,bigdig/vnpy,harveywwu/vnpy,andrewchenshx/vnpy,harveywwu/vnpy,harveywwu/vnpy,msincenselee/vnpy,rrrrrr8/vnpy,andrewchenshx/vnpy,rrrrrr8/vnpy,harveywwu/vnpy,rrrrrr8/vnpy,vnpy/vnpy,rrrrrr8/vnpy,msincenselee/vnpy,bigdig/vnpy,bigdig/vnpy,vnpy/vnpy,bigdig/vnpy,andrewchenshx/vnpy,rrrrrr8/vnpy,harveywwu/vnpy,msincenselee/vnpy,rrrrrr8/vnpy