[glass] Don't check IsConnected for NT widgets (#4674)

Checking this isn't required, and prevented these widgets from working
in the simulation GUI without another NT client connected.

glass/src/libnt/native/cpp/NTField2D.cpp

@@ -171,7 +171,7 @@ void NTField2DModel::Update() {
 }
 
 bool NTField2DModel::Exists() {
-  return m_inst.IsConnected() && m_nameTopic.Exists();
+  return m_nameTopic.Exists();
 }
 
 bool NTField2DModel::IsReadOnly() {