resolve: add Utils.methodNotAllowed

- Switch to 405 / method not allowed in InstanceHandler

Author: Twinki14

api/src/main/java/xyz/gianlu/librespot/api/Utils.java

@@ -83,4 +83,9 @@ public static void internalError(@NotNull HttpServerExchange exchange, @NotNull
         exchange.setStatusCode(StatusCodes.INTERNAL_SERVER_ERROR);
         exchange.getResponseSender().send(String.format(INTERNAL_ERROR_BODY, reason));
     }
+
+    public static void methodNotAllowed(@NotNull HttpServerExchange exchange) {
+        exchange.setStatusCode(StatusCodes.METHOD_NOT_ALLOWED);
+        exchange.getResponseSender().send(StatusCodes.METHOD_NOT_ALLOWED_STRING);
+    }
 }

api/src/main/java/xyz/gianlu/librespot/api/handlers/InstanceHandler.java

@@ -104,7 +104,7 @@ protected void handleRequest(@NotNull HttpServerExchange exchange, @NotNull Sess
                             session.close();
                             break;
                         default:
-                            Utils.invalidParameter(exchange, "action");
+                            Utils.methodNotAllowed(exchange);
                             break;
                     }
                     break;
@@ -150,7 +150,7 @@ protected void handleRequest(@NotNull HttpServerExchange exchange, @NotNull Sess
                             session.close();
                             break;
                         default:
-                            Utils.invalidParameter(exchange, "action");
+                            Utils.methodNotAllowed(exchange);
                             break;
                     }
                     break;