Fix data race on errs slice

[s4ymur]

Problem

The following scenario is possible and it is leads to data race:

1. In recover() branch wait group is released
2. Then it is possible to read errs
3. But at the same time other goroutine still can write to errs

Thus Race Detector catches concurrent read-write.

Proposed solution

Call wg.Done() by defer. Then the algorithm will look as follows:

1. Write to errs
2. wg.Done()
3. Read errs

In this solution reads go strictly after writes.