Singularity tweaks

Fix an off-by-one error that caused the singulo to get stuck along contaiment fields. For a 5x5 singulo, it would check 6 squares ahead (correct for a step forward) and then 6 squares to the sides (incorrect). Now it tests 6 squares ahead, 5 to the sides. This is technically wrong for the growth checks but they check every direction anyways, so it's ok.
Made the singularity drift in all cases and not stop next to lattices.
In process(), moved the growth checks after the movement attempt so it will take a step and then grow rather than take a step, drift into the walls, and then attempt and fail to grow as part of the next process().
Merge pull request #5719 from MrPerson/pls_dont_make_fun_of_the_singulo_shes_not_fat_just_big_boned

Singularity tweaks