GPU: Fix segfault when copying to Vulkan swapchain (#15543)

(cherry picked from commit 76f8705c12)

src/gpu/vulkan/SDL_gpu_vulkan.c

@@ -2452,6 +2452,11 @@ static void VULKAN_INTERNAL_TrackTextureTransfer(
     VulkanCommandBuffer *commandBuffer,
     VulkanTexture *texture)
 {
+    // Textures not managed by our allocator (i.e. the swapchain) don't need to be refcounted.
+    if (texture->usedRegion == NULL) {
+        return;
+    }
+
     TRACK_RESOURCE(
         texture,
         VulkanTexture *,