Print error if p12 was empty/failed to parse

main.go

@@ -212,6 +212,9 @@ func getCerts(reader io.Reader, filename string, format string) ([]certWithAlias
 		if err != nil {
 			return nil, err
 		}
+		if len(blocks) == 0 {
+			return nil, fmt.Errorf("keystore appears to be empty or password was incorrect")
+		}
 		for _, block := range blocks {
 			if block.Type == "CERTIFICATE" {
 				cert, err := x509.ParseCertificate(block.Bytes)