Flush stdout prior of calling render stats callback

Without this extra flush order of stat prints is undefined in the
output. which makes it rather tricky to write custom output in a
reliable way.

source/blender/render/intern/source/pipeline.c

@@ -193,6 +193,9 @@ static void stats_background(void *UNUSED(arg), RenderStats *rs)
 			fprintf(stdout, IFACE_("Sce: %s Ve:%d Fa:%d La:%d"), rs->scene_name, rs->totvert, rs->totface, rs->totlamp);
 	}
 
+	/* Flush stdout to be sure python callbacks are printing stuff after blender. */
+	fflush(stdout);
+
 	BLI_callback_exec(G.main, NULL, BLI_CB_EVT_RENDER_STATS);
 
 	fputc('\n', stdout);
@@ -3436,7 +3439,10 @@ static int do_write_image_or_movie(Render *re, Main *bmain, Scene *scene, bMovie
 	
 	BLI_timestr(re->i.lastframetime, name, sizeof(name));
 	printf(" Time: %s", name);
-	
+
+	/* Flush stdout to be sure python callbacks are printing stuff after blender. */
+	fflush(stdout);
+
 	BLI_callback_exec(G.main, NULL, BLI_CB_EVT_RENDER_STATS);
 
 	BLI_timestr(re->i.lastframetime - render_time, name, sizeof(name));