[Core] Add missing file to Core project;

Author: LittleCodingFox

Engine/Staple.Core/Staple.Core.csproj

@@ -199,6 +199,7 @@
 		<Compile Include="Rendering\RenderSystem\Backend\Impls\SDLGPU\Commands\SDLGPUDestroyIndexBufferCommand.cs" />
 		<Compile Include="Rendering\RenderSystem\Backend\Impls\SDLGPU\Commands\SDLGPUDestroyTextureCommand.cs" />
 		<Compile Include="Rendering\RenderSystem\Backend\Impls\SDLGPU\Commands\SDLGPUDestroyVertexBufferCommand.cs" />
+		<Compile Include="Rendering\RenderSystem\Backend\Impls\SDLGPU\Commands\SDLGPUReadTextureCommand.cs" />
 		<Compile Include="Rendering\RenderSystem\Backend\Impls\SDLGPU\Commands\SDLGPURenderCommand.cs" />
 		<Compile Include="Rendering\RenderSystem\Backend\Impls\SDLGPU\Commands\SDLGPURenderTransientCommand.cs" />
 		<Compile Include="Rendering\RenderSystem\Backend\Impls\SDLGPU\Commands\SDLGPURenderTransientUIntCommand.cs" />