Revert "Optimization: simplify fill_surfaces before the offset operation"

To workaround issue #1325 and possibly #1320.

This reverts commit 3a046e34111aeaf3701062f006e9f5957635e15b.

lib/Slic3r/Layer/Region.pm

@@ -209,11 +209,12 @@ 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 },
-            offset2_ex(
-                [ map $_->simplify(&Slic3r::SCALED_RESOLUTION), @last ],
-                -($perimeter_spacing/2 + $infill_spacing),
-                +$infill_spacing,
-            );
+            map $_->simplify(&Slic3r::SCALED_RESOLUTION),
+                offset2_ex(
+                    \@last,
+                    -($perimeter_spacing/2 + $infill_spacing),
+                    +$infill_spacing,
+                );
     }
     
     $self->_fill_gaps(\@gaps);