Fix jumping hidden items larger than the bed after hitting arrange

src/slic3r/GUI/Jobs/ArrangeJob.cpp

@@ -239,7 +239,9 @@ void ArrangeJob::finalize(bool canceled, std::exception_ptr &eptr) {
     
     // Move the unprintable items to the last virtual bed.
     for (ArrangePolygon &ap : m_unprintable) {
+        if (ap.bed_idx >= 0)
             ap.bed_idx += beds + 1;
+
         ap.apply();
     }