Fix warnings when running on null renderer

Source/Engine/Render2D/FontTextureAtlas.cpp

@@ -222,7 +222,7 @@ void FontTextureAtlas::Flush()
 
 void FontTextureAtlas::EnsureTextureCreated() const
 {
-    if (_texture->IsAllocated() == false)
+    if (_texture->IsAllocated() == false && GPUDevice::Instance->GetRendererType() != RendererType::Null)
     {
         // Initialize atlas texture
         if (_texture->Init(GPUTextureDescription::New2D(_width, _height, 1, _format, GPUTextureFlags::ShaderResource)))

Source/Engine/UI/GUI/RenderOutputControl.cs

@@ -220,7 +220,9 @@ namespace FlaxEngine.GUI
                 width = _customResolution.Value.X;
                 height = _customResolution.Value.Y;
             }
-            if (_backBuffer == null || _backBuffer.Width == width && _backBuffer.Height == height)
+            if (_backBuffer == null || (_backBuffer.Width == width && _backBuffer.Height == height))
+                return;
+            if (GPUDevice.Instance.RendererType == RendererType.Null)
                 return;
             if (width < 1 || height < 1)
             {