fix color bleeding on border drawing

Fixes https://forum.lvgl.io/t/border-dont-cover-calendar/3029/4

CHANGELOG.md

@@ -10,6 +10,9 @@
 - Add `lv_font_free()` function - Frees the memory allocated by the `lv_font_load()` function
 - Add style caching to reduce acces time of properties with default value
 
+### Bugfixes
+- Fix color bleeding on border drawing
+
 ## v7.3.1 (18.08.2020)
 
 ### Bugfixes

src/lv_core/lv_obj.c

@@ -3801,7 +3801,7 @@ static lv_design_res_t lv_obj_design(lv_obj_t * obj, const lv_area_t * clip_area
         lv_draw_rect_dsc_init(&draw_dsc);
         /*If the border is drawn later disable loading its properties*/
         if(lv_obj_get_style_border_post(obj, LV_OBJ_PART_MAIN)) {
-            draw_dsc.border_opa = LV_OPA_TRANSP;
+            draw_dsc.border_post = 1;
         }
 
         lv_obj_init_draw_rect_dsc(obj, LV_OBJ_PART_MAIN, &draw_dsc);

src/lv_draw/lv_draw_rect.c

@@ -391,6 +391,7 @@ LV_ATTRIBUTE_FAST_MEM static void draw_border(const lv_area_t * coords, const lv
     if(dsc->border_opa <= LV_OPA_MIN) return;
     if(dsc->border_width == 0) return;
     if(dsc->border_side == LV_BORDER_SIDE_NONE) return;
+    if(dsc->border_post) return;
 
     int32_t coords_w = lv_area_get_width(coords);
     int32_t coords_h = lv_area_get_height(coords);

src/lv_draw/lv_draw_rect.h

@@ -41,6 +41,7 @@ typedef struct {
     lv_style_int_t border_side;
     lv_opa_t border_opa;
     lv_blend_mode_t border_blend_mode;
+    uint8_t border_post :1;         /*There is a border it will be drawn later. */
 
     /*Outline*/
     lv_color_t outline_color;