ecore_wl2: purge surface buffers in semi_free

Summary:
This fixes a session recovery bug with software render.

An attempt to re-use a buffer in a new wayland connection resulted
in another disconnect and broken rendering.
Depends on D6281

Reviewers: devilhorns, zmike

Reviewed By: zmike

Subscribers: cedric, #committers, zmike

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D6282

src/lib/ecore_wl2/ecore_wl2_window.c

@@ -41,6 +41,8 @@ _ecore_wl2_window_semi_free(Ecore_Wl2_Window *window)
 
    window->outputs = eina_list_free(window->outputs);
 
+   ecore_wl2_window_surface_flush(window, EINA_TRUE);
+
    window->commit_pending = EINA_FALSE;
 }