[gegl] buffer: add gegl_tile_needs_store() internal function

[Ell <ell src gnome org>]

commit bf6dd78e256e1a59d1504e7ba4193a150bd18377
Author: Ell <ell_se yahoo com>
Date:   Sun Dec 2 09:30:28 2018 -0500

    buffer: add gegl_tile_needs_store() internal function
    
    ... which determines if a tile will be needs to be stored.  This is
    a slightly stronger condition than ! gegl_tile_is_stored():  a tile
    needs to be stored if it has an associated tile-storage, is
    unstored, and is undamaged.

 gegl/buffer/gegl-buffer-private.h |  1 +
 gegl/buffer/gegl-tile.c           | 12 ++++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)
---
diff --git a/gegl/buffer/gegl-buffer-private.h b/gegl/buffer/gegl-buffer-private.h
index 69ecefbd1..102502322 100644
--- a/gegl/buffer/gegl-buffer-private.h
+++ b/gegl/buffer/gegl-buffer-private.h
@@ -187,6 +187,7 @@ struct _GeglTile
   gpointer         unlock_notify_data;
 };
 
+gboolean gegl_tile_needs_store    (GeglTile *tile);
 void     gegl_tile_unlock_no_void (GeglTile *tile);
 gboolean gegl_tile_damage         (GeglTile *tile,
                                    guint64   damage);
diff --git a/gegl/buffer/gegl-tile.c b/gegl/buffer/gegl-tile.c
index b7dc76f2d..bbedefd65 100644
--- a/gegl/buffer/gegl-tile.c
+++ b/gegl/buffer/gegl-tile.c
@@ -383,6 +383,14 @@ gegl_tile_is_stored (GeglTile *tile)
   return tile->stored_rev == tile->rev;
 }
 
+gboolean
+gegl_tile_needs_store (GeglTile *tile)
+{
+  return tile->tile_storage           &&
+         ! gegl_tile_is_stored (tile) &&
+         ! tile->damage;
+}
+
 void
 gegl_tile_void (GeglTile *tile)
 {
@@ -418,7 +426,7 @@ gboolean gegl_tile_store (GeglTile *tile)
   gboolean ret;
   if (gegl_tile_is_stored (tile))
     return TRUE;
-  if (tile->tile_storage == NULL || tile->damage)
+  else if (! gegl_tile_needs_store (tile))
     return FALSE;
 
   g_rec_mutex_lock (&tile->tile_storage->mutex);
@@ -426,7 +434,7 @@ gboolean gegl_tile_store (GeglTile *tile)
   if (gegl_tile_is_stored (tile))
     {
       g_rec_mutex_unlock (&tile->tile_storage->mutex);
-      return FALSE;
+      return TRUE;
     }
 
   ret = gegl_tile_source_set_tile (GEGL_TILE_SOURCE (tile->tile_storage),