Fix Javadoc in AcceptHeaderLocaleResolver

[m1stake]

Affects: spring-webmvc 5.1.6.RELEASE

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org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver.setDefaultLocale, line 74

// ...
// By default this is not set in which case when there is "Accept-Language" header 
// ...
public void setDefaultLocale(@Nullable Locale defaultLocale) { ... }

I think it means "when there is no 'Accept-Language' header".

[sbrannen]

This has been fixed in master.

Thanks