cmd/compile: fix open defer of method call

Code generation for open defers failed to account for
presence of method receiver and thus was OFF BY ONE.

Fixes #45062.
Updates #44816.
Updates #40724.

Change-Id: Ia90ea8fd0f7d823e1f757c406f9127136c2ffdd2
Reviewed-on: https://go-review.googlesource.com/c/go/+/302249


Trust: David Chase <drchase@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>