AudioWorkgroup: Fix an issue with copying objects in an objective-c block

modules/juce_audio_plugin_client/juce_audio_plugin_client_AU_1.mm

@@ -406,8 +406,8 @@ public:
 
                #if JUCE_AUDIOWORKGROUP_TYPES_AVAILABLE
                 case kAudioUnitProperty_RenderContextObserver:
-                    outWritable = false;
                     outDataSize = sizeof (AURenderContextObserver);
+                    outWritable = false;
                     return noErr;
                #endif
 
@@ -584,14 +584,15 @@ public:
                #if JUCE_AUDIOWORKGROUP_TYPES_AVAILABLE
                 case kAudioUnitProperty_RenderContextObserver:
                 {
-                    if (auto* ptr = (AURenderContextObserver*) outData)
+                    AURenderContextObserver callback = ^(const AudioUnitRenderContext* context)
                     {
-                        *ptr = contextObserver;
-                        return noErr;
-                    }
+                        jassert (juceFilter != nullptr);
+                        const auto workgroup = makeRealAudioWorkgroup (context != nullptr ? context->workgroup : nullptr);
+                        juceFilter->audioWorkgroupContextChanged (workgroup);
+                    };
 
-                    jassertfalse;
-                    break;
+                    *(AURenderContextObserver*) outData = [callback copy];
+                    return noErr;
                 }
                #endif
 
@@ -2027,17 +2028,6 @@ private:
     HeapBlock<bool> pulledSucceeded;
     HeapBlock<MIDIPacketList> packetList { packetListBytes, 1 };
 
-   #if JUCE_AUDIOWORKGROUP_TYPES_AVAILABLE
-    ObjCBlock<AURenderContextObserver> contextObserver { ^(const AudioUnitRenderContext* context)
-    {
-        if (juceFilter == nullptr)
-            return;
-
-        auto workgroup = makeRealAudioWorkgroup (context != nullptr ? context->workgroup : nullptr);
-        juceFilter->audioWorkgroupContextChanged (std::move (workgroup));
-    } };
-   #endif
-
     ThreadLocalValue<bool> inParameterChangedCallback;
 
     AudioProcessorChangedUpdater audioProcessorChangedUpdater { *this };