Locking the Aseprite data moving behind a mutex.

This should squish the last data races around this part.

The lock policy is simple:
- The `AsepriteConnection` locks the data when it has to write a frame
- The main thread will try to lock to not block the whole update/render
  loop.

src/AsepriteConnection.cpp

@@ -57,7 +57,11 @@ void AsepriteConnection::onMessage(std::shared_ptr<ix::ConnectionState> connecti
                     newImage.pixels.emplace_back(nextByte);
                     data += 4;
                 }
-                lastReadyImage = std::move(newImage);
+
+                {
+                    std::scoped_lock imageLock(lastReadyImageMutex);
+                    lastReadyImage = std::move(newImage);                
+                }
             }
         }
         break;

src/AsepriteConnection.h

@@ -9,6 +9,7 @@
 #include <cstdint>
 #include <memory>
 #include <vector>
+#include <mutex>
 
 struct AsepriteImage
 {
@@ -25,6 +26,7 @@ struct AsepriteImage
 
 struct AsepriteConnection
 {
+    mutable std::mutex lastReadyImageMutex;
     AsepriteImage lastReadyImage;
     bool connected = false;
 

src/main.cpp

@@ -179,7 +179,12 @@ int start()
             else
             {
                 ClearBackground(darkBackground ? DARKGRAY : WHITE);
-                AsepriteImage lastImage = std::move(imageServer.lastReadyImage);
+                AsepriteImage lastImage; 
+                if (imageServer.lastReadyImageMutex.try_lock())
+                {
+                    lastImage = std::move(imageServer.lastReadyImage);
+                    imageServer.lastReadyImageMutex.unlock();
+                }
                 Image currentImage;
                 currentImage.width = lastImage.width;
                 currentImage.height = lastImage.height;