lost logs when append data quickly after truncate

[HeChuanXUPT]

config

tail.Config{
	Follow:    true,
	Poll:      true,
	ReOpen:    false,
	MustExist: true,
	Location: &tail.SeekInfo{0, os.SEEK_END}})

case 1, OK

$ echo "test log 1" >> test.log
$ >test.log
$ echo "test log 2" >> test.log

can get 2 lines

case 2, MISS

$ echo "test log 1" >> test.log
$ >test.log && echo "test log 2" >> test.log

will miss the second log

env

system：windows 7 64bit
branch: master