go/types: don't panic in complex division
Make sure that in complex division we reject divisors that would
underflow to zero when using the textbook complex-division method we
currently use.
This change does for go/types what golang.org/cl/42650 did for gc.
Fixes #20227
Change-Id: Iaa784ac5e60141f51c501eb0e3ce0e9c1c2993d0
Reviewed-on: https://go-review.googlesource.com/44590
Run-TryBot: Alberto Donizetti <alb.donizetti@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>