cmd/compile: fix problem with non-decomposed vars
cmd/compile: fix problem with non-decomposed vars

Fix a bug introduced in patch 2 of
https://go-review.googlesource.com/72630 (sense of a map
lookup test was accidentally flipped).

Change-Id: Icc6096ee50be4605fa7542b9fd855c13b8aff090
Reviewed-on: https://go-review.googlesource.com/72850
Run-TryBot: Than McIntosh <4b2922593166fc595a9b1a408f34f5d3817fe9d2@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>

nawawi/go,codestation/go,nawawi/go,codestation/go,cloudflare/go,Cofyc/go,akutz/go,josharian/go,codestation/go,akutz/go,golang/go,akutz/go,CAFxX/go,josharian/go,CAFxX/go,golang/go,akutz/go,cloudflare/go,akutz/go,cloudflare/go,akutz/go,codestation/go,codestation/go,nawawi/go,Cofyc/go,Cofyc/go,CAFxX/go,Cofyc/go,CAFxX/go,CAFxX/go,Cofyc/go,nawawi/go,CAFxX/go,josharian/go,josharian/go,josharian/go,akutz/go,nawawi/go,christopher-henderson/Go,golang/go,codestation/go,golang/go,cloudflare/go,josharian/go,Cofyc/go,golang/go,golang/go,josharian/go,Cofyc/go,cloudflare/go,nawawi/go,golang/go,codestation/go,akutz/go,Cofyc/go,cloudflare/go,nawawi/go,golang/go,josharian/go,CAFxX/go,nawawi/go,cloudflare/go,cloudflare/go,CAFxX/go,codestation/go