Fix chamfer tab missing from cap in "all" preview mode

The clipping cube used to intersect the cap started at X=0 in the cap's
local frame, clipping out the chamfer tab which extends to -_cap_gap_w.
Shift the cube origin back by _cap_gap_w and widen it to match.

cable_cap.scad

@@ -259,8 +259,8 @@ if (PART == "case") {
             translate([case_w - CAP_ENGAGE + CAP_EXPLODE, 0, 0])
                 intersection() {
                     cable_cap();
-                    translate([0, 0, -(CAP_TOL + CAP_WALL)])
-                        cube([CAP_ENGAGE + CAP_WALL + 1,
+                    translate([-_cap_gap_w, 0, -(CAP_TOL + CAP_WALL)])
+                        cube([CAP_ENGAGE + CAP_WALL + 1 + _cap_gap_w,
                               _clip[1],
                               case_h + 2*(CAP_TOL + CAP_WALL) + 1]);
                 }