wl_egl: check is_activated after calling can_dequeue

wl_egl: check is_activated after calling can_dequeue

 - to resolve regression issue related to support frontbuffer rendering mode.
 - The issue was caused by the commit below

    wl_egl: remove checking activated when dequeue buffer
    c362b0b2860d1ebab098956e2567aeef8313952c

     - Actual buffer will be attached when calling tbm_surface_queue_can_dequeue().
      So calling wayland_tbm_client_queue_check_activate() at dequeue_buffer
      is not appropriate.

Change-Id: I88b58a62bc42537d7bd8fe1d446a343fd40aab7b
Signed-off-by: Joonbum Ko <joonbum.ko@samsung.com>