proto/add: avoid panic when using non-hierarchical path (#829)

cmd/kratos/internal/proto/add/add.go

@@ -21,6 +21,10 @@ func run(cmd *cobra.Command, args []string) {
 	// kratos add helloworld/v1/helloworld.proto
 	input := args[0]
 	n := strings.LastIndex(input, "/")
+	if n == -1 {
+		fmt.Println("The proto path needs to be hierarchical.")
+		return
+	}
 	path := input[:n]
 	fileName := input[n+1:]
 	pkgName := strings.ReplaceAll(path, "/", ".")