Use copy of va_list rather than original va_list in txt_set_text_vfmt (#1890)
Use copy of va_list rather than original va_list in txt_set_text_vfmt (#1890)

Fix issue #1886

Co-authored-by: Wenting Zhang <888a30873f6742a5fc5d7ed33a447747b3c52b6f@outlook.com>
littlevgl/lvgl,littlevgl/lvgl,littlevgl/lvgl,littlevgl/lvgl