Convolution: Fix issue where old convolution engines were sometimes u…

…sed after calling prepare

The startThread/stopThread calls were moved to prevent a thread
sanitizer warning about a race on the vtable of Impl.

modules/juce_dsp/frequency/juce_Convolution.cpp

@@ -77,14 +77,7 @@ class BackgroundMessageQueue  : private Thread
 public:
     explicit BackgroundMessageQueue (int entries)
         : Thread ("Convolution background loader"), queue (entries)
-    {
-        startThread();
-    }
-
-    ~BackgroundMessageQueue() override
-    {
-        stopThread (-1);
-    }
+    {}
 
     using IncomingCommand = FixedSizeFunction<400, void()>;
 
@@ -93,6 +86,9 @@ class BackgroundMessageQueue  : private Thread
     // This function is only safe to call from a single thread at a time.
     bool push (IncomingCommand& command) { return queue.push (command); }
 
+    using Thread::startThread;
+    using Thread::stopThread;
+
 private:
     void run() override
     {
@@ -119,9 +115,14 @@ ConvolutionMessageQueue::ConvolutionMessageQueue()
 
 ConvolutionMessageQueue::ConvolutionMessageQueue (int entries)
     : pimpl (std::make_unique<Impl> (entries))
-{}
+{
+    pimpl->startThread();
+}
 
-ConvolutionMessageQueue::~ConvolutionMessageQueue() noexcept = default;
+ConvolutionMessageQueue::~ConvolutionMessageQueue() noexcept
+{
+    pimpl->stopThread (-1);
+}
 
 ConvolutionMessageQueue::ConvolutionMessageQueue (ConvolutionMessageQueue&&) noexcept = default;
 ConvolutionMessageQueue& ConvolutionMessageQueue::operator= (ConvolutionMessageQueue&&) noexcept = default;
@@ -1016,7 +1017,8 @@ class Convolution::Impl
     {
         mixer.prepare (spec);
         engineQueue->prepare (spec);
-        installPendingEngine();
+        currentEngine = engineQueue->getEngine();
+        previousEngine = nullptr;
         jassert (currentEngine != nullptr);
     }