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

Most likely introduced here: #11006
{
    const ColumnFixedString & src = assert_cast<const ColumnFixedString &>(src_);
    if (n != src.getN())
        throw Exception("Size of FixedString doesn't match", ErrorCodes::SIZE_OF_FIXED_STRING_DOESNT_MATCH);
    size_t old_size = chars.size();
    chars.resize(old_size + n);
    memcpySmallAllowReadWriteOverflow15(chars.data() + old_size, &src.chars[n * index], n);
}
void ColumnFixedString::insertData(const char * pos, size_t length)
{
    if (length > n)
        throw Exception("Too large string 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, pos, length);
}
StringRef ColumnFixedString::serializeValueIntoArena(size_t index, Arena & arena, char const *& begin) const
{
    auto * pos = arena.allocContinue(n, begin);
    memcpy(pos, &chars[n * index], n);
    return StringRef(pos, n);
}
const char * ColumnFixedString::deserializeAndInsertFromArena(const char * pos)
{
    size_t old_size = chars.size();
    chars.resize(old_size + n);
    memcpy(chars.data() + old_size, pos, n);
    return pos + n;
}
void ColumnFixedString::updateHashWithValue(size_t index, SipHash & hash) const