[online_image] Clear LVGL dsc when image size changes. (#15360)

esphome/components/runtime_image/runtime_image.cpp

@@ -247,6 +247,9 @@ void RuntimeImage::release_buffer_() {
     this->height_ = 0;
     this->buffer_width_ = 0;
     this->buffer_height_ = 0;
+#ifdef USE_LVGL
+    memset(&this->dsc_, 0, sizeof(this->dsc_));
+#endif
   }
 }