Wayland: Fix glfwPostEmptyEvent leaking a proxy

The client-side proxy of the callback from each call to wl_display_sync
was never destroyed.

Fixes #2836

CONTRIBUTORS.md

@@ -57,6 +57,7 @@ video tutorials.
  - Jason Daly
  - danhambleton
  - Jarrod Davis
+ - Aaron Day
  - decce
  - Olivier Delannoy
  - Paul R. Deppe

README.md

@@ -155,6 +155,7 @@ information on what to include when reporting a bug.
  - [Wayland] Bugfix: Mouse wheel scroll distance was incorrect on some compositors
  - [Wayland] Bugfix: `glfwSwapBuffers` would halt with nonzero swap interval when window
    was suspended (#1350,#2582,#2640,#2719,#2723,#2800,#2827)
+ - [Wayland] Bugfix: `glfwPostEmptyEvent` would leak a callback proxy (#2836)
  - [X11] Bugfix: Running without a WM could trigger an assert (#2593,#2601,#2631)
  - [X11] Bugfix: Occasional crash when an idle display awakes (#2766) 
  - [X11] Bugfix: Prevent BadWindow when creating small windows with a content scale

src/wl_window.c

@@ -199,6 +199,16 @@ static struct wl_buffer* createShmBuffer(const GLFWimage* image)
     return buffer;
 }
 
+static void callbackHandleDone(void* userData, struct wl_callback* callback, uint32_t data)
+{
+    wl_callback_destroy(callback);
+}
+
+static const struct wl_callback_listener noopCallbackListener =
+{
+    callbackHandleDone
+};
+
 static void createFallbackEdge(_GLFWwindow* window,
                                _GLFWfallbackEdgeWayland* edge,
                                struct wl_surface* parent,
@@ -2930,7 +2940,9 @@ void _glfwWaitEventsTimeoutWayland(double timeout)
 
 void _glfwPostEmptyEventWayland(void)
 {
-    wl_display_sync(_glfw.wl.display);
+    struct wl_callback* callback = wl_display_sync(_glfw.wl.display);
+    wl_callback_add_listener(callback, &noopCallbackListener, NULL);
+
     flushDisplay();
 }