grt: erase destroyed net from dirty set in CUGR path

GlobalRouter::removeNet only erased the net from dirty_nets_ in the
FastRoute (non-CUGR) branch. When use_cugr_ is true, a net destroyed
during incremental routing stayed in dirty_nets_, so updateDirtyRoutes
later passed the dangling dbNet to CUGR::updateNet, which dereferenced
it via Design::updateNet (db_net->getSigType()).

In release builds (NDEBUG) this use-after-free is silent, so
grt.incremental_deleted_net.tcl passed. With assertions enabled
(coverage / RELEASEWITHASSERTS builds) the stale sig type tripped
dbSigType::isSupply()'s assert(false) and aborted.

Move the dirty_nets_.erase to run for both routers.

Signed-off-by: Matt Liberty <mliberty@precisioninno.com>

Author: maliberty

src/grt/src/GlobalRouter.cpp

@@ -4799,6 +4799,10 @@ void GlobalRouter::removeNet(odb::dbNet* db_net)
     return;
   }
 
+  // Drop the destroyed net from the dirty set for both routers so
+  // updateDirtyRoutes never dereferences a dangling dbNet.
+  dirty_nets_.erase(db_net);
+
   if (use_cugr_) {
     cugr_->removeNet(db_net);
   } else {
@@ -4858,7 +4862,6 @@ void GlobalRouter::removeNet(odb::dbNet* db_net)
     }
     delete deleted_net;
     db_net_map_.erase(db_net);
-    dirty_nets_.erase(db_net);
     routes_.erase(db_net);
   }
 }