image: use Rectangle{} instead of ZR
ZR is deprecated,
so replace it with the literal Rectangle to represent the zero value.
Change-Id: I68c0ffec808eaed1e8c352bf364d295c0041594e
GitHub-Last-Rev:
850472888d3d0f5e68feb9ec09f0b544fe1f9446
GitHub-Pull-Request: golang/go#69136
Reviewed-on: https://go-review.googlesource.com/c/go/+/609516
Reviewed-by: Nigel Tao <nigeltao@golang.org>
Reviewed-by: Nigel Tao <nigeltao@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>