FIX Replace substr with mb_substr to get the correct position

[lhalaa]

Example content:

We're using DBText::ContextSummary() for search results and noticed that the summary didn't contain the keywords. This is due to not returning the correct position when extracting texts from a multibyte string. This fix will update the remaining substr to mb_substr.

[robbieaverill]

LGTM

[michalkleiner]

A change that makes sense, but at the same time, is it a change in the public API/current vs future behaviour?

[ScopeyNZ]

A change that makes sense, but at the same time, is it a change in the public API/current vs future behaviour?

Considering the existing use of multibyte safe string functions I think it's incredibly unlikely that this would be breaking any existing functionality. It's certainly not affecting public API.

Thanks for the PR @lhalaa

[michalkleiner]

Just for my clarification, maybe I understand API changes differently — When I update a patch version and the frontend starts returning different content, that's not consider public API change? Or maybe not an API, but external behaviour change.

[robbieaverill]

Usually the public API refers to public functions in our PHP code. Behavioural changes are considered also, but if a change fixes a bug it’s better to do it than to reject it and have people rely on broken behaviour.