MessageManager: Obey the rule of useful return in callAsync

modules/juce_events/messages/juce_MessageManager.cpp

@@ -184,16 +184,16 @@ void* MessageManager::callFunctionOnMessageThread (MessageCallbackFunction* func
     return nullptr;
 }
 
-void MessageManager::callAsync (std::function<void()> fn)
+bool MessageManager::callAsync (std::function<void()> fn)
 {
     struct AsyncCallInvoker  : public MessageBase
     {
-        AsyncCallInvoker (std::function<void()> f) : callback (std::move (f)) { post(); }
+        AsyncCallInvoker (std::function<void()> f) : callback (std::move (f)) {}
         void messageCallback() override  { callback(); }
         std::function<void()> callback;
     };
 
-    new AsyncCallInvoker (std::move (fn));
+    return (new AsyncCallInvoker (std::move (fn)))->post();
 }
 
 //==============================================================================

modules/juce_events/messages/juce_MessageManager.h

@@ -94,8 +94,12 @@ public:
    #endif
 
     //==============================================================================
-    /** Asynchronously invokes a function or C++11 lambda on the message thread. */
-    static void callAsync (std::function<void()> functionToCall);
+    /** Asynchronously invokes a function or C++11 lambda on the message thread.
+
+        @returns  true if the message was successfully posted to the message queue,
+                  or false otherwise.
+    */
+    static bool callAsync (std::function<void()> functionToCall);
 
     /** Calls a function using the message-thread.