fix: batch flush method

[jonyhy96]

Fixes #475

Motivation

Fix wrong batch flush method bug.

Modifications

Check if batchBuilder is multi batches before flush.

Verifying this change

• Make sure that the change passes the CI checks.

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

If yes was chosen, please highlight the changes

• Dependencies (does it add or upgrade a dependency): no
• The public API: no
• The schema: no
• The default values of configurations: no
• The wire protocol: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? GoDocs

[jonyhy96]

/cc @wolfstudy @freeznet

[jonyhy96]

There is a data race happens in the ci test. Should i fix it before merged or we could issue another pr for this?

[freeznet]

There is a data race happens in the ci test. Should i fix it before merged or we could issue another pr for this?

i think we should fix the ci test issue in another pr.

[wolfstudy]

There is a data race happens in the ci test. Should i fix it before merged or we could issue another pr for this?

Thanks @jonyhy96 work for this, please fix the ci error or send new pull request to fix this, thanks.

And please make sure to create one issue to track this, thanks.

[jonyhy96]

There is a data race happens in the ci test. Should i fix it before merged or we could issue another pr for this?

Thanks @jonyhy96 work for this, please fix the ci error or send new pull request to fix this, thanks.

And please make sure to create one issue to track this, thanks.

The ci error is not caused by this pr. Maybe someone else can fix it.

[jonyhy96]

The data race condition in ci test happens occasionally, as we can see the checks of this pr is all passed 😅
I issued this problem in #483.
/cc @freeznet @wolfstudy

[wolfstudy]

Cool Thanks @jonyhy96