encoding/xml: use reflect.Value.IsZero
IsZero does the same thing, using this rather than writing it again.
Change-Id: I62810ac2d1a6e189feac03b022c8931fb6993e19
GitHub-Last-Rev:
1d5fd10d96baf75e8b170a2c71949ff3d0884c46
GitHub-Pull-Request: golang/go#63519
Reviewed-on: https://go-review.googlesource.com/c/go/+/534935
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>