Adding a directory with read-only or corrupt files returns an unhelpful error

#### Version information:

go-ipfs version: 0.4.22-rc1-39a71fe75
Repo version: 7
System version: amd64/linux
Golang version: go1.12.7

#### Description:

**To reproduce:**

1. Create a directory with several reasonably sized files.
2. Use `chmod` to make one of these files unreadable.
3. Try adding the directory.

**Expected results:**

IPFS fails with something like "failed to read file X"

**Actual results:**

> Error: read tcp 192.168.0.116:33916->192.168.0.165:5001: use of closed network connection

**Cause:**

This is due to an upstream bug: https://github.com/golang/go/issues/11745. The real error is getting swallowed by a different error.

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replaces https://github.com/ipfs/go-ipfs/issues/3855