Fix of a "split" function issue.

1) Load a multi-part stl
2) Rotate it by 90 degrees
3) Split it.

Before this fix, the split object jumped away from the print bed.

This sound similar to
https://github.com/prusa3d/Slic3r/issues/309

lib/Slic3r/GUI/Plater.pm

@@ -1158,6 +1158,8 @@ sub split_object {
         $self->resume_background_process;
         return;
     }
+    
+    $_->center_around_origin for (@model_objects);
 
     $self->remove($obj_idx);
     $current_object = $obj_idx = undef;