Handle errors from printLineAndFlush function

Updated the printLineAndFlush function to return an error instead of terminating the program. Modified the main function to handle the error appropriately by logging the error and exiting when printLineAndFlush fails.

main.go

@@ -49,7 +49,11 @@ func main() {
 			fmt.Println(err)
 			os.Exit(-1)
 		}
-		println(jwt)
+		err = printLineAndFlush(jwt)
+		if err != nil {
+			fmt.Println(err)
+			os.Exit(-1)
+		}
 	case "test-cert <uzi> <ura> <agb>", "test-cert <uzi> <ura> <agb> <subject_did>":
 		// Format is 2.16.528.1.1007.99.2110-1-900030787-S-90000380-00.000-11223344
 		// <OID CA>-<versie-nr>-<UZI-nr>-<pastype>-<Abonnee-nr>-<rol>-<AGB-code>
@@ -94,26 +98,27 @@ func main() {
 			fmt.Println(err)
 			os.Exit(-1)
 		}
-		printLineAndFlush(jwt)
+		err = printLineAndFlush(jwt)
+		if err != nil {
+			fmt.Println(err)
+			os.Exit(-1)
+		}
 	default:
 		fmt.Println("Unknown command")
 		os.Exit(-1)
 	}
 }
 
 // printLineAndFlush writes a JWT (JSON Web Token) to the standard output and flushes the buffered writer.
-func printLineAndFlush(jwt string) {
+func printLineAndFlush(jwt string) error {
 	f := bufio.NewWriter(os.Stdout)
 	// Make sure to flush
 	defer func(f *bufio.Writer) {
 		_ = f.Flush()
 	}(f)
 	// Write the JWT
 	_, err := f.WriteString(jwt + "\n")
-	if err != nil {
-		fmt.Println(err)
-		os.Exit(-1)
-	}
+	return err
 }
 
 func issueVc(vc VC) (string, error) {