Revert "Optimization: simplify fill_surfaces before the offset operation"

To workaround issue #1325 and possibly #1320.

This reverts commit 3a046e3411.

lib/Slic3r/Layer/Region.pm

@@ -209,8 +209,9 @@ sub make_perimeters {
         # and then we offset back and forth by the infill spacing to only consider the
         # non-collapsing regions
         push @{ $self->fill_surfaces },
+            map $_->simplify(&Slic3r::SCALED_RESOLUTION),
                 offset2_ex(
-                [ map $_->simplify(&Slic3r::SCALED_RESOLUTION), @last ],
+                    \@last,
                     -($perimeter_spacing/2 + $infill_spacing),
                     +$infill_spacing,
                 );