/particle’s dx dy dz behaves inconsistently with selector’s

/particle’s dx dy dz extends to both the postive and negative compared to the origin; rather than only postive if the number is postive, or negative if the number is negative.

This is inconsistent with the selector’s dx dy dz values, where the origin is always in one of the corners.

For example:

particle flame 0 0 0 1 1 0

will spread the particle in -1,-1,0 to 1,1,0 rather than 0,0,0 to 1,1,0.