HeAP: Skip high-strength cells in both cell loops.

Previously only the first loop skipped cells with high belStrength,
but they can't be processed by the second loop either, so skip them
there too.

common/placer_heap.cc

@@ -1322,6 +1322,10 @@ class HeAPPlacer
                     continue;
                 }
 
+                if (cell.belStrength > STRENGTH_STRONG) {
+                    continue;
+                }
+
                 // Transfer chain extents to the actual chains structure
                 ChainExtent *ce = nullptr;
                 if (p->chain_root.count(cell_name)) {