ImGui: Shortcuts Not working
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* **What is the current behaviour?**
Pressing Ctrl+O does not print `Open` (by not activating the `Open` menu item).

* **Please provide the steps to reproduce and if possible a minimal demo of the problem**
```nim
import nimgl/imgui, nimgl/imgui/[impl_opengl, impl_glfw]
import nimgl/[opengl, glfw]

proc main() =
  doAssert glfwInit()

  glfwWindowHint(GLFWContextVersionMajor, 3)
  glfwWindowHint(GLFWContextVersionMinor, 3)
  glfwWindowHint(GLFWOpenglForwardCompat, GLFW_TRUE)
  glfwWindowHint(GLFWOpenglProfile, GLFW_OPENGL_CORE_PROFILE)
  glfwWindowHint(GLFWResizable, GLFW_FALSE)

  var w: GLFWWindow = glfwCreateWindow(1280, 720)
  if w == nil:
    quit(-1)

  w.makeContextCurrent()

  doAssert glInit()

  let context = igCreateContext()

  doAssert igGlfwInitForOpenGL(w, true)
  doAssert igOpenGL3Init()

  igStyleColorsCherry()

  while not w.windowShouldClose:
    glfwPollEvents()

    igOpenGL3NewFrame()
    igGlfwNewFrame()
    igNewFrame()

    # Simple window
    igBegin("Hello, world!", flags = MenuBar)

    if igBeginMenuBar():
      if igBeginMenu("File"):
        if igMenuItem("Open", "Ctrl+O"):
          echo "Open"
        igEndMenu()
      igEndMenuBar()

    igEnd()
    # End simple window

    igRender()

    glClearColor(0.45f, 0.55f, 0.60f, 1.00f)
    glClear(GL_COLOR_BUFFER_BIT)

    igOpenGL3RenderDrawData(igGetDrawData())

    w.swapBuffers()

  igOpenGL3Shutdown()
  igGlfwShutdown()
  context.igDestroyContext()

  w.destroyWindow()
  glfwTerminate()

main()
```

* **What is the expected behaviour?**
`Open` being printed when pressing Ctrl+O.

* **Please tell us about your environment**

  - Version: 1.3.2
  - OS: Linux
  - Bindings: ImGui
  - Backend: CPP]
  - Nim Version: 1.6.5
  - Compiler used: GCC

* **Other information** (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow, docs.gl, documentation etc)
`igMenuItem(label: cstring, shortcut: cstring = nil, ...)`https://nimgl.dev/docs/imgui.html#igMenuItem%2Ccstring%2Ccstring%2Cbool%2Cbool
