Fixed|UI|Multiplayer: Potential crash when joining an MP game

Synchronous signal handling (game unload, MP join) may lead to the
widget being gone when it's time to check if there's a further
action to do.

IssueID #1954

doomsday/client/src/ui/widgets/gameselectionwidget.cpp

@@ -460,13 +460,16 @@ void GameSelectionWidget::updateSubsetLayout()
 void GameSelectionWidget::select(ui::Item const *item)
 {
     if(!item) return;
-
+
+    // Should we perform an action afterwards? The signal handling may lead to
+    // destruction of the widget, so we'll hold a ref to the action.
+    AutoRef<Action> postAction(d->doAction? makeAction(*item) : nullptr);
+
+    // Notify.
     emit gameSessionSelected(item);
-
-    // Should we also perform the action?
-    if(d->doAction)
+
+    if(bool(postAction))
     {
-        AutoRef<Action> act = makeAction(*item);
-        act->trigger();
+        postAction->trigger();
     }
 }

doomsday/libcore/include/de/data/counted.h

@@ -237,6 +237,7 @@ template <typename CountedType>
 class AutoRef
 {
 public:
+    AutoRef() : _ref(nullptr) {}
     AutoRef(CountedType *preHeld) : _ref(preHeld) {}
     AutoRef(CountedType &ref) : _ref(holdRef(ref)) {}
     ~AutoRef() { releaseRef(_ref); }
@@ -248,6 +249,7 @@ class AutoRef
     operator CountedType * () { return _ref; }
     operator CountedType const & () const { return *_ref; }
     operator CountedType & () { return *_ref; }
+    explicit operator bool () const { return _ref != nullptr; }
 private:
     CountedType *_ref;
 };