[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/NTDigitalOutput.cpp

@@ -40,5 +40,5 @@ void NTDigitalOutputModel::Update() {
 }
 
 bool NTDigitalOutputModel::Exists() {
-  return m_inst.IsConnected() && m_value.Exists();
+  return m_value.Exists();
 }