Wayland: Fix duplicate monitor connection events

GLFW would report a monitor as connected each time its wl_output
received an update, for example if its scale changed.

This would also cause the monitor to be added to the monitor array
again, causing glfwTerminate to segfault when it attempted to destroy
its already destroyed wl_output.

(cherry picked from commit c3ad3d49ed)

src/wl_monitor.c

@@ -95,6 +95,12 @@ static void outputHandleDone(void* userData, struct wl_output* output)
         monitor->heightMM = (int) (mode->height * 25.4f / 96.f);
     }
 
+    for (int i = 0; i < _glfw.monitorCount; i++)
+    {
+        if (_glfw.monitors[i] == monitor)
+            return;
+    }
+
     _glfwInputMonitor(monitor, GLFW_CONNECTED, _GLFW_INSERT_LAST);
 }