It seems that xlog not closed correctly when watchdog fired

[Michael Filonenko]

Repro:

require('watchdog').start(3)
box.cfg{}
box.schema.create_space('test')
box.space.test:create_index('pkey')
box.space.test:put({1, 2}) while true do local i = 1 end

watchdog fired

box.cfg{}

recover from `./00000000000000000000.xlog'
file `./00000000000000000000.xlog` wasn't correctly closed

It does not affect data, but affects human log analyze events