cmd/vulnreport: return after create

Adds a return statement after create and create-excluded command so
that a fatal usage error is not logged.

Change-Id: I351f8d92d8aac8049ff8283403054db73747fa65
Reviewed-on: https://go-review.googlesource.com/c/vulndb/+/459642
Reviewed-by: Tatiana Bradley <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Tatiana Bradley <[email protected]>
Reviewed-by: Julie Qiu <[email protected]>

Author: tatianab

cmd/vulnreport/main.go

@@ -124,6 +124,7 @@ func main() {
 				}
 			}
 		}
+		return
 	}
 
 	ghsaClient := ghsa.NewClient(ctx, *githubToken)