Setting ImGuiContext for ImPlot

Author: TillAlex

src/ImGui.NET.SampleProgram/ImGuiController.cs

@@ -63,6 +63,7 @@ public ImGuiController(GraphicsDevice gd, OutputDescription outputDescription, i
             ImGui.SetCurrentContext(context);
             IntPtr implotContext = ImPlot.CreateContext();
             ImPlot.SetCurrentContext(implotContext);
+            ImPlot.SetImGuiContext(context);
             var fonts = ImGui.GetIO().Fonts;
             ImGui.GetIO().Fonts.AddFontDefault();