image/tiff: fix a panic with invalid tile sizes

Fuzzing detected that an invalid tile size could cause a
panic. Fix a typo in the range check to solve it.

Fixes golang/go#10712.

Change-Id: I88a5a7884d98f622cc89ed6e394becebb07c6e60
Reviewed-on: https://go-review.googlesource.com/11020
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2 files changed