manager注册计时器中的崩溃问题

[GenesisAN]

ZeroBot-Plugin/plugin/manager/timer/timer.go

Lines 64 to 74 in 5cd46b3

	var ctx *zero.Ctx
	if ts.SelfID != 0 {
	ctx = zero.GetBot(ts.SelfID)
	} else {
	zero.RangeBot(func(id int64, c *zero.Ctx) bool {
	ctx = c
	ts.SelfID = id
	return false
	})
	}
	eid, err := c.cron.AddFunc(ts.Cron, func() { ts.sendmsg(ts.GrpID, ctx) })

该ctx的获取于66行，而这导致该值只会在注册命令时获取，因此在重启机器人后，由cron触发的第74行的sendMsg代码中的ctx将为空，这将导致整个机器人崩溃。在发送前重新获取ctx可避免该问题。不知道作者是否有别的修复建议

发生异常: panic
"runtime error: invalid memory address or nil pointer dereference"
Stack:
	4  0x00000000009d247a in github.com/FloatTech/ZeroBot-Plugin/plugin/manager/timer.(*Timer).sendmsg
	    at [c:/Code/go/ZeroBot-Plugin/plugin/manager/timer/msg.go:9]()
	5  0x00000000009d6a88 in github.com/FloatTech/ZeroBot-Plugin/plugin/manager/timer.(*Clock).RegisterTimer.func2
	    at [c:/Code/go/ZeroBot-Plugin/plugin/manager/timer/timer.go:75]()
	6  0x0000000000941f1f in github.com/fumiama/cron.FuncJob.Run
	    at [C:/Users/AN/go/pkg/mod/github.com/fumiama/cron]()@v1.3.0/cron.go:135
	7  0x0000000000944108 in github.com/fumiama/cron.(*Cron).startJob.func1
	    at [C:/Users/AN/go/pkg/mod/github.com/fumiama/cron]()@v1.3.0/cron.go:361