[ndnSIM] table: Workaround for cases of lookup using a detached PIT entry

Change-Id: Id93feea542e8b6309e4357a3fc6c692522d871e7
diff --git a/daemon/table/measurements.cpp b/daemon/table/measurements.cpp
index 247a584..8573d3f 100644
--- a/daemon/table/measurements.cpp
+++ b/daemon/table/measurements.cpp
@@ -81,8 +81,11 @@
 Measurements::get(const pit::Entry& pitEntry)
 {
   shared_ptr<name_tree::Entry> nte = m_nameTree.get(pitEntry);
+  // a workaround for PIT entry deleted from PIT, but still alive as an object
+  if (nte == nullptr) {
+    return nullptr;
+  }
 
-  BOOST_ASSERT(nte != nullptr);
   return this->get(*nte);
 }
 
diff --git a/daemon/table/name-tree.cpp b/daemon/table/name-tree.cpp
index 8e699c5..981bf43 100644
--- a/daemon/table/name-tree.cpp
+++ b/daemon/table/name-tree.cpp
@@ -324,6 +324,10 @@
 NameTree::get(const pit::Entry& pitEntry)
 {
   shared_ptr<name_tree::Entry> nte = pitEntry.m_nameTreeEntry;
+  if (nte == nullptr) {
+    return nullptr;
+  }
+
   if (nte->getPrefix().size() == pitEntry.getName().size()) {
     return nte;
   }