Update condition for post worker VK

... after the refactor in aosp/2589626.

Bug: b/242184599
Test: cvd start --gpu_mode=gfxstream_guest_angle_host_swiftshader
Change-Id: I47626e17fca3a64442bf0c24b3d0794be41ca053
GitOrigin-RevId: 0d76e113cea0b68840ab06e5638e21f4b8602414
diff --git a/host/FrameBuffer.cpp b/host/FrameBuffer.cpp
index fac9562..2fb1c7c 100644
--- a/host/FrameBuffer.cpp
+++ b/host/FrameBuffer.cpp
@@ -427,10 +427,11 @@
     INFO("Graphics API Extensions %s", fb->m_graphicsApiExtensions.c_str());
     INFO("Graphics Device Extensions %s", fb->m_graphicsDeviceExtensions.c_str());
 
-    bool shouldPostOnlyOnMainThread = postOnlyOnMainThread();
-    if (fb->m_displayVk) {
+    if (fb->m_useVulkanComposition) {
         fb->m_postWorker.reset(new PostWorkerVk(fb.get(), fb->m_compositor, fb->m_displayVk));
     } else {
+        const bool shouldPostOnlyOnMainThread = postOnlyOnMainThread();
+
         PostWorkerGl* postWorkerGl =
             new PostWorkerGl(shouldPostOnlyOnMainThread, fb.get(), fb->m_compositor,
                              fb->m_emulationGl->getFakeWindowSurface(), fb->m_displayGl);