D3D12: Fix GetCompletedValue() returning hardcoded 0

Was returning 0 unconditionally. Now correctly returns
m_frameFence->GetCompletedValue() to report GPU progress.

engine/src/RHI/D3D12/D3D12CommandQueue.cpp

@@ -104,6 +104,9 @@ void D3D12CommandQueue::Wait(ID3D12Fence* fence, uint64_t value) {
 }
 
 uint64_t D3D12CommandQueue::GetCompletedValue() {
+    if (m_frameFence) {
+        return m_frameFence->GetCompletedValue();
+    }
     return 0;
 }