[BUG] spiral_sweep lead_in does not work as expected

[pipatron]

In spiral_sweep(), lead_in2 does nothing and lead_in1 works as the plain lead_in argument:

spiral_sweep(rect(5),30,10,2,lead_in=5);
spiral_sweep(rect(5),30,10,2,lead_in1=5);
spiral_sweep(rect(5),30,10,2,lead_in2=5);

lead_in=5	lead_in1=5	lead_in2=5

I get different breakage with lead_in_ang:

spiral_sweep(rect(5),30,10,2,lead_in_ang=20);
spiral_sweep(rect(5),30,10,2,lead_in_ang1=20);
spiral_sweep(rect(5),30,10,2,lead_in_ang2=20);

lead_in_ang=20	lead_in_ang1=20	lead_in_ang2=20

The missing render comes with this error message:

ERROR: Assertion '(is_num(v) || is_vector(v))' failed: "Invalid scale" in file ../../openscad/lib/BOSL2/transforms.scad, line 822 TRACE: called by 'scale' in file ../../openscad/lib/BOSL2/skin.scad, line 1311 TRACE: called by 'spiral_sweep' in file ../../openscad/lib/BOSL2/skin.scad, line 1334 TRACE: assignment to 'vnf' in file ../../openscad/lib/BOSL2/skin.scad, line 1334 TRACE: called by 'spiral_sweep' in file old_headphone_inlet.scad, line 6

[adrianVmariano]

I think I have this fixed in the PR.