VideoCommon: Don't create pipelines with no render targets

Some backends don't like it when you do that

Source/Core/VideoCommon/PostProcessing.cpp

@@ -709,6 +709,9 @@ bool PostProcessing::CompilePixelShader()
 
 bool PostProcessing::CompilePipeline()
 {
+  if (m_framebuffer_format == AbstractTextureFormat::Undefined)
+    return true;  // Not needed (some backends don't like making pipelines with no targets)
+
   AbstractPipelineConfig config = {};
   config.vertex_shader = m_vertex_shader.get();
   config.geometry_shader =

Source/Core/VideoCommon/RenderBase.cpp

@@ -1068,6 +1068,13 @@ bool Renderer::InitializeImGui()
 
 bool Renderer::RecompileImGuiPipeline()
 {
+  if (m_backbuffer_format == AbstractTextureFormat::Undefined)
+  {
+    // No backbuffer (nogui) means no imgui rendering will happen
+    // Some backends don't like making pipelines with no render targets
+    return true;
+  }
+
   std::unique_ptr<AbstractShader> vertex_shader =
       CreateShaderFromSource(ShaderStage::Vertex, FramebufferShaderGen::GenerateImGuiVertexShader(),
                              "ImGui vertex shader");