fix: Truncate utf8 only at code point boundaries (#2699)

### Problem description
<!-- Describe the bug that you fixed/feature request that you
implemented, or link to an existing issue describing it -->
There are utf8 sequences passed to the logging code which contains
invalid utf8 code points. This causes an exception, which is catched,
but the log is not correct as a result. The cause is truncating strings
without regard for mutibyte code points.

See [here](https://github.com/WerWolv/ImHex/issues/2697) for the issue.

### Implementation description
Added a function to truncate utf8 strings correctly to
[libwolv](https://github.com/WerWolv/libwolv/pull/39) and used it in
some troublesome places.

Fixes #2697