fix window_manager_paint_normal for fragment lcd

docs/changes.md

@@ -1,4 +1,7 @@
 # 最新动态
+* 2020/02/04
+  * 片段 lcd 的片段内存大小刚好等于脏矩形大小的问题（感谢智明提供补丁）
+
 * 2020/01/28
   * 优化list view paint children
   * 增加emitter\_forward

src/window_manager/window_manager_default.c

@@ -640,6 +640,9 @@ static ret_t window_manager_paint_normal(widget_t* widget, canvas_t* c) {
           tmp_h = h % tmp_h;
         }
         r.h = tmp_h;
+        if (r.h == 0) {
+          break;
+        }
 
         canvas_t* c = native_window_get_canvas(wm->native_window);
         canvas_begin_frame(c, &r, LCD_DRAW_NORMAL);