cmd/compile: use the zero value for results of impossible indexing
type A [0]int
var a A
x := a[i]
Use the zero value for x instead of the "impossible" value. That lets
us at least compile code like this with -B, even though it can't
possibly run correctly.
Fixes #48092
Change-Id: Idad5cfab49e05f375c069b05addceed68a15299f
Reviewed-on: https://go-review.googlesource.com/c/go/+/346589
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org> Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>