Vulkan: Avoid duplicate image pre-transitions (actually eliminated later anyway, but a small saving)

ext/native/thin3d/VulkanRenderManager.cpp

@@ -687,6 +687,12 @@ VkImageView VulkanRenderManager::BindFramebufferAsTexture(VKRFramebuffer *fb, in
 		}
 	}
 
+	if (!curRenderStep_->preTransitions.empty() &&
+			curRenderStep_->preTransitions.back().fb == fb &&
+			curRenderStep_->preTransitions.back().targetLayout == VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL) {
+		// We're done.
+		return fb->color.imageView;
+	}
 	curRenderStep_->preTransitions.push_back({ fb, VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL });
 	return fb->color.imageView;
 }