cmd/govulncheck: do not shadow err in doGovulncheck.

Removes shadowing of the err variable in doGovulncheck.
May be involved with the nil pointer dereference in golang/go#56689.

Updates golang/go#56689

Change-Id: I805c9106f08dffda73efcd04e7a418b0ac8f64d2
Reviewed-on: https://go-review.googlesource.com/c/vuln/+/449675
Reviewed-by: Jonathan Amsterdam <jba@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Zvonimir Pavlinovic <zpavlinovic@google.com>
Run-TryBot: Tim King <taking@google.com>
diff --git a/cmd/govulncheck/main.go b/cmd/govulncheck/main.go
index 1df8011..38825a5 100644
--- a/cmd/govulncheck/main.go
+++ b/cmd/govulncheck/main.go
@@ -99,7 +99,8 @@
 	cfg := &govulncheck.Config{Client: dbClient}
 	var res *govulncheck.Result
 	if sourceAnalysis {
-		pkgs, err := loadPackages(patterns, dir)
+		var pkgs []*vulncheck.Package
+		pkgs, err = loadPackages(patterns, dir)
 		if err != nil {
 			// Try to provide a meaningful and actionable error message.
 			if !fileExists(filepath.Join(dir, "go.mod")) {
@@ -115,7 +116,8 @@
 		}
 		res, err = govulncheck.Source(ctx, cfg, pkgs)
 	} else {
-		f, err := os.Open(patterns[0])
+		var f *os.File
+		f, err = os.Open(patterns[0])
 		if err != nil {
 			return err
 		}