Add mapping for the space key.

src/ImGui.NET.SampleProgram/ImGuiController.cs

@@ -413,6 +413,7 @@ namespace ImGuiNET
             io.KeyMap[(int)ImGuiKey.Backspace] = (int)Key.BackSpace;
             io.KeyMap[(int)ImGuiKey.Enter] = (int)Key.Enter;
             io.KeyMap[(int)ImGuiKey.Escape] = (int)Key.Escape;
+            io.KeyMap[(int)ImGuiKey.Space] = (int)Key.Space;
             io.KeyMap[(int)ImGuiKey.A] = (int)Key.A;
             io.KeyMap[(int)ImGuiKey.C] = (int)Key.C;
             io.KeyMap[(int)ImGuiKey.V] = (int)Key.V;