Don't delete busy E_Comp_Wl_Buffers

Hardware planes are going to make E_Comp_Wl_Buffer lifetimes harder to
manage, so we need to let the E_Comp_Wl_Buffer object outlive the
resource attached to it.

We already track a busy count, so we just have to use it to prevent
deleting a busy buffer.

src/bin/e_comp_wl.c

@@ -1010,7 +1010,10 @@ _e_comp_wl_buffer_cb_destroy(struct wl_listener *listener, void *data EINA_UNUSE
 
    buffer = container_of(listener, E_Comp_Wl_Buffer, destroy_listener);
    wl_signal_emit(&buffer->destroy_signal, buffer);
-   free(buffer);
+   buffer->destroyed = EINA_TRUE;
+
+   if (!buffer->busy)
+     free(buffer);
 }
 
 static void

src/bin/e_comp_wl.h

@@ -63,6 +63,7 @@ struct _E_Comp_Wl_Buffer
    E_Pixmap *discarding_pixmap;
    int32_t w, h;
    uint32_t busy;
+   Eina_Bool destroyed;
 };
 
 struct _E_Comp_Wl_Surface_State

src/bin/e_pixmap.c

@@ -144,6 +144,12 @@ _e_pixmap_wl_resource_release(E_Comp_Wl_Buffer *buffer)
         buffer->pool = NULL;
      }
 
+   if (buffer->destroyed)
+     {
+        free(buffer);
+        return;
+     }
+
    wl_resource_queue_event(buffer->resource, WL_BUFFER_RELEASE);
 }