fix(themes): Fix mono theme init (#8343)

src/display/lv_display.c

@@ -127,6 +127,13 @@ lv_display_t * lv_display_create(int32_t hor_res, int32_t ver_res)
     else {
         disp->theme = lv_theme_simple_get();
     }
+#elif LV_USE_THEME_MONO
+    if(lv_theme_mono_is_inited() == false) {
+        disp->theme = lv_theme_mono_init(disp, false, LV_FONT_DEFAULT);
+    }
+    else {
+        disp->theme = lv_theme_mono_get();
+    }
 #endif
 
     disp->bottom_layer = lv_obj_create(NULL); /*Create bottom layer on the display*/

src/themes/mono/lv_theme_mono.c

@@ -515,6 +515,14 @@ static void theme_apply(lv_theme_t * th, lv_obj_t * obj)
 #endif
 }
 
+lv_theme_t * lv_theme_mono_get(void)
+{
+    if(!lv_theme_mono_is_inited()) {
+        return NULL;
+    }
+    return (lv_theme_t *)theme_def;
+}
+
 /**********************
  *   STATIC FUNCTIONS
  **********************/

src/themes/mono/lv_theme_mono.h

@@ -44,6 +44,12 @@ lv_theme_t * lv_theme_mono_init(lv_display_t * disp, bool dark_bg, const lv_font
 */
 bool lv_theme_mono_is_inited(void);
 
+/**
+ * Get mono theme
+ * @return a pointer to mono theme, or NULL if this is not initialized
+ */
+lv_theme_t * lv_theme_mono_get(void);
+
 /**
  * Deinitialize the mono theme
  */