Fix partial image update during rendering

Was broken since 5d212fb.

source/blender/editors/render/render_internal.c

@@ -893,6 +893,7 @@ static int screen_render_invoke(bContext *C, wmOperator *op, const wmEvent *even
 	rj->write_still = is_write_still && !is_animation;
 	rj->iuser.scene = scene;
 	rj->iuser.ok = 1;
+	rj->iuser.passtype = SCE_PASS_COMBINED;
 	rj->reports = op->reports;
 	rj->orig_layer = 0;
 	rj->last_layer = 0;