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: 8504728
GitHub-Pull-Request: #69136
Reviewed-on: https://go-review.googlesource.com/c/go/+/609516
Reviewed-by: Nigel Tao <[email protected]>
Reviewed-by: Nigel Tao <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: tomocy

src/image/geom.go

@@ -169,7 +169,7 @@ func (r Rectangle) Intersect(s Rectangle) Rectangle {
 	//
 	// if max(r0.Min.X, s0.Min.X) >= min(r0.Max.X, s0.Max.X) || likewiseForY { etc }
 	if r.Empty() {
-		return ZR
+		return Rectangle{}
 	}
 	return r
 }