Add handling of missing HOME env

+ drawapp.cpp : added checking if env HOME exists
+ if not draw3 is launched in read-only mode for user drawdefinable sets

wx/draw3/drawapp.cpp

@@ -314,9 +314,19 @@ bool DrawApp::OnInit() {
 	//wxLog *logger = new wxLogGui();
 	wxLog::SetActiveTarget(logger);
 
-	std::string home_path = getenv("HOME");
-	m_instance = std::make_unique<FileLocker>(home_path + "/.draw3_defined_lock");
-	m_instance->checkLockCorrectness();
+	if(getenv("HOME") != nullptr) {
+		std::string home_path = getenv("HOME");
+		if(home_path.empty() == false) {
+			m_instance = std::make_unique<FileLocker>(home_path + "/.draw3_defined_lock");
+			m_instance->checkLockCorrectness();
+		}
+		else {
+			m_instance = nullptr;
+		}
+	}
+	else {
+		m_instance = nullptr;
+	}
 
 	SetMaxCoreDumpLimit();
 	InitGL();
@@ -607,6 +617,11 @@ bool DrawApp::OnCmdLineParsed(wxCmdLineParser &parser) {
 }
 
 void DrawApp::CheckActiveInstance() {
+	if(m_instance == nullptr) {
+		read_only = true;
+		return;
+	}
+
 	if (m_instance->tryLocking()) {
 		read_only = false;
 	} else {