ipfs repo gc streaming errors bug

Odd test failure:

```
expecting success:
test_must_fail ipfs repo gc --stream-errors 2>&1 | tee repo_gc_out &&
grep -q "Error: could not retrieve links for $LEAF1" repo_gc_out &&
grep -q "Error: could not retrieve links for $LEAF2" repo_gc_out &&
grep -q "Error: garbage collection aborted" repo_gc_out

Error: could not retrieve links for QmSijovevteoY63Uj1uC5b8pkpDU5Jgyk2dYBqz3sMJUPc: merkledag: not found
Error: could not retrieve links for QmTbPEyrA1JyGUHFvmtx1FNZVzdBreMv8Hc8jV9sBRWhNA: The block referred to by 'QmTbPEyrA1JyGUHFvmtx1FNZVzdBreMv8Hc8jV9sBRWhNA' was not a valid merkledag node
Error: json: cannot unmarshal number into Go value of type commands.GcResult

not ok 48 - 'ipfs repo gc --stream-errors' should abort and report each error separately

#
# test_must_fail ipfs repo gc --stream-errors 2>&1 | tee repo_gc_out &&
# grep -q "Error: could not retrieve links for $LEAF1" repo_gc_out &&
# grep -q "Error: could not retrieve links for $LEAF2" repo_gc_out &&
# grep -q "Error: garbage collection aborted" repo_gc_out
```

My guess would be an HTTP streaming bug. We may be reading out the final trailing 0 length as an actual result.