Fixed regression when concentric infill was used as solid infill. Includes regression test. #1650

lib/Slic3r/Fill/Concentric.pm

@@ -28,7 +28,7 @@ sub fill_surface {
         $flow = Slic3r::Flow->new_from_spacing(
             spacing             => unscale($distance),
             nozzle_diameter     => $flow->nozzle_diameter,
-            layer_height        => $surface->thickness,
+            layer_height        => ($params{layer_height} or die "No layer_height supplied to fill_surface()"),
             bridge              => $flow->bridge,
         );
     }