**Describe the bug**
https://clickhouse-test-reports.s3.yandex.net/19702/c74631c650b42e4d107254a03bd82c2c2913039b/fuzzer_msan/server.log

Most likely introduced here: #11006
{
    MutableColumnPtr new_col_holder = ColumnFixedString::create(n);
    if (size > 0)
    {
        auto & new_col = assert_cast<ColumnFixedString &>(*new_col_holder);
        new_col.chars.resize(size * n);
        size_t count = std::min(this->size(), size);
        memcpy(new_col.chars.data(), chars.data(), count * n * sizeof(chars[0]));
        if (size > count)
            memset(&(new_col.chars[count * n]), '\0', (size - count) * n);
    }
    return new_col_holder;
}
void ColumnFixedString::insert(const Field & x)
{
    const String & s = DB::get<const String &>(x);
    if (s.size() > n)
        throw Exception("Too large string '" + s + "' for FixedString column", ErrorCodes::TOO_LARGE_STRING_SIZE);
    size_t old_size = chars.size();
    chars.resize_fill(old_size + n);
    memcpy(chars.data() + old_size, s.data(), s.size());
}
void ColumnFixedString::insertFrom(const IColumn & src_, size_t index)