stt: coverity fixes

Signed-off-by: Eder Monteiro <[email protected]>

Author: eder-matheus

src/stt/src/SteinerTreeBuilder.cpp

@@ -202,6 +202,10 @@ void SteinerTreeBuilder::setMinHPWLAlpha(int min_hpwl, float alpha)
 
 int SteinerTreeBuilder::computeHPWL(odb::dbNet* net)
 {
+  if (net->getBTermCount() + net->getITermCount() == 0) {
+    return 0;
+  }
+
   int min_x = std::numeric_limits<int>::max();
   int min_y = std::numeric_limits<int>::max();
   int max_x = std::numeric_limits<int>::min();

src/stt/src/flt/flute.cpp

@@ -1323,7 +1323,7 @@ Tree Flute::flutes_MD(int d,
 
       std::vector<int> tmp_ys(ys.begin() + d - 1 - ms, ys.end());
       t2 = flutes_LMD(ms + 1, xs, tmp_ys, s2, acc);
-      t = dmergetree(t1, t2);
+      t = dmergetree(std::move(t1), std::move(t2));
 
       free(score);
       free(penalty);