go/packages: check error in addNeededOverlayPackages

Change-Id: I65e4817da00695007fa62554e61ff4d61c19eb44
Reviewed-on: https://go-review.googlesource.com/c/tools/+/183988
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/go/packages/golist.go b/go/packages/golist.go
index 04c6396..320d566 100644
--- a/go/packages/golist.go
+++ b/go/packages/golist.go
@@ -213,7 +213,9 @@
 	if err != nil {
 		return err
 	}
-	addNeededOverlayPackages(cfg, driver, response, needPkgs)
+	if err := addNeededOverlayPackages(cfg, driver, response, needPkgs); err != nil {
+		return err
+	}
 	return nil
 }