fail to validate after update acl

[yuz10]

BUG REPORT

1. Please describe the issue you observed:

• What did you do (The steps to reproduce)?

1. call updateAccessConfig to update acl
2. do acl validation using the new acl

• What did you expect to see?

• What did you see instead?
  see the error:

java.lang.NullPointerException
	at org.apache.rocketmq.acl.plain.PlainPermissionManager.validate(PlainPermissionManager.java:646)
	at org.apache.rocketmq.acl.plain.PlainAccessValidator.validate(PlainAccessValidator.java:141)
	at org.apache.rocketmq.acl.plain.PlainAccessValidatorTest.testValidateAfterUpdateAccessConfig(PlainAccessValidatorTest.java:942)

4. Please tell us about your environment:

5. Other information (e.g. detailed explanation, logs, related issues, suggestions how to fix, etc):
   after update acl, the file watcher will call load() function, the plainAccessResourceMap will not put new acl because the condition this.accessKeyTable.get(plainAccessResource.getAccessKey()) is not null

                if (this.accessKeyTable.get(plainAccessResource.getAccessKey()) == null) {
                    plainAccessResourceMap.put(plainAccessResource.getAccessKey(), plainAccessResource);
                    this.accessKeyTable.put(plainAccessResource.getAccessKey(), aclFilePath);
                }