When dragging the right edge, don't consider the left offset and vice versa
When dragging the right edge, don't consider the left offset and vice versa

This is to fix a bug that when moving the right edge towards left, the selection box doesn't get smaller beyond a certain width because Math.max was considering the left offset when it gets smaller than the actual displacement, and vice versa.

Ensembl/ensembl-webcode,Ensembl/ensembl-webcode,Ensembl/ensembl-webcode,Ensembl/ensembl-webcode,Ensembl/ensembl-webcode