[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/NetworkTables.cpp

@@ -552,7 +552,7 @@ void NetworkTablesModel::RebuildTreeImpl(std::vector<TreeNode>* tree,
 }
 
 bool NetworkTablesModel::Exists() {
-  return m_inst.IsConnected();
+  return true;
 }
 
 NetworkTablesModel::Entry* NetworkTablesModel::GetEntry(std::string_view name) {