Move bridge detection to its own method

lib/Slic3r/Layer/Region.pm

@@ -517,7 +517,12 @@ sub process_external_surfaces {
     }
     
     # detect bridge direction (skip bottom layer)
-    if ($self->id > 0) {
+    $self->_detect_bridges if $self->id > 0;
+}
+
+sub _detect_bridges {
+    my $self = shift;
+    
     my @bottom  = grep $_->surface_type == S_TYPE_BOTTOM, @{$self->fill_surfaces};  # surfaces
     my @lower   = @{$self->layer->object->layers->[ $self->id - 1 ]->slices};       # expolygons
     
@@ -626,6 +631,5 @@ sub process_external_surfaces {
         $surface->bridge_angle($bridge_angle);
     }
 }
-}
 
 1;