fix: Safely capture this as weak_ptr

Author: mrousavy

package/cpp/ListenerManager.h

@@ -8,18 +8,31 @@
 #include <algorithm>
 #include <functional>
 #include <list>
+#include <memory>
 
 namespace margelo {
 
-template <typename Callback> class ListenerManager {
+template <typename Callback> class ListenerManager : public std::enable_shared_from_this<ListenerManager<Callback>> {
 private:
+  using TSelf = ListenerManager<Callback>;
   std::list<Callback> _listeners;
 
+private:
+  std::shared_ptr<ListenerManager<Callback>> shared() {
+    return this->shared_from_this();
+  }
+
 public:
   Listener add(Callback listener) {
     _listeners.push_back(std::move(listener));
     auto id = --_listeners.end();
-    return Listener([id, this]() { _listeners.erase(id); });
+    auto weakThis = std::weak_ptr<TSelf>(shared());
+    return Listener([id, weakThis]() {
+      auto sharedThis = weakThis.lock();
+      if (sharedThis) {
+        sharedThis->_listeners.erase(id);
+      }
+    });
   }
 
   const std::list<Callback>& getListeners() {