Update Bricks.cpp

[jamierobertson1]

Fixes a bug in "divide_round" which resulted in incorrect keys being calculated for negative values falling on divisor boundaries.

    auto divide_round = [](int64_t value, int64_t divisor) -> int64_t {
        if (value < 0)
            return -1 - (-value / divisor);
        else
            return value / divisor;
    };

For example if value is -256 and divisor is 256, this would return a key of -2, when it should be the first entry in key -1

This resulted in artifacts on pointclouds with negative coordinates.

proposed fix is:

        if (value < 0)
            return -1 + (value + 1) / divisor;