[UI/D3D12] Small refactoring, allow BeginSwap to return false if no surface

src/xenia/ui/vulkan/vulkan_context.cc

@@ -141,7 +141,7 @@ bool VulkanContext::MakeCurrent() {
 
 void VulkanContext::ClearCurrent() {}
 
-void VulkanContext::BeginSwap() {
+bool VulkanContext::BeginSwap() {
   SCOPE_profile_cpu_f("gpu");
   auto provider = static_cast<VulkanProvider*>(provider_);
   auto device = provider->device();
@@ -170,6 +170,8 @@ void VulkanContext::BeginSwap() {
   // TODO(benvanik): use a fence instead? May not be possible with target image.
   std::lock_guard<std::mutex> queue_lock(device->primary_queue_mutex());
   status = vkQueueWaitIdle(device->primary_queue());
+
+  return true;
 }
 
 void VulkanContext::EndSwap() {