drt: Do not check upper layer property when we are on the last metal.

Signed-off-by: Christian Costa <titan.costa@gmail.com>

Author: titan73

src/drt/src/gc/FlexGC_main.cpp

@@ -3801,7 +3801,8 @@ void FlexGCWorker::Impl::patchMetalShape_minStep()
     auto layer = tech_->getLayer(lNum);
     if (!layer->hasVia2ViaMinStepViol()
         && !tech_->getLayer(lNum - 1)->hasLef58MaxSpacingConstraints()
-        && !tech_->getLayer(lNum + 1)->hasLef58MaxSpacingConstraints()) {
+        && (lNum + 1 >= tech_->getLayers().size()
+            || !tech_->getLayer(lNum + 1)->hasLef58MaxSpacingConstraints())) {
       continue;
     }