Optimization: don't store wipe path if wipe is not requested

lib/Slic3r/Print.pm

@@ -711,7 +711,7 @@ sub write_gcode {
     # set up our extruder object
     my $gcodegen = Slic3r::GCode->new(
         config              => $self->config,
-        multiple_extruders  => (@{$self->extruders} > 1),
+        extruders           => $self->extruders,
         layer_count         => $self->layer_count,
     );
     print $fh "G21 ; set units to millimeters\n" if $Slic3r::Config->gcode_flavor ne 'makerware';