fix(grid,flex): fix compile errors when grid or flex is disabled (#5289)

demos/render/lv_demo_render.c

@@ -9,6 +9,7 @@
 #include "lv_demo_render.h"
 
 #if LV_USE_DEMO_RENDER
+
 #include "../../src/display/lv_display_private.h"
 #include "../../src/core/lv_global.h"
 

demos/render/lv_demo_render.h

@@ -17,6 +17,10 @@ extern "C" {
 
 #if LV_USE_DEMO_RENDER
 
+#if LV_USE_GRID == 0
+#error "LV_USE_GRID needs to be enabled"
+#endif
+
 /*********************
  *      DEFINES
  *********************/