fix(txt): no need to add null ending after snprintf (#4265)

Signed-off-by: Xu Xingliang <xuxingliang@xiaomi.com>

src/misc/lv_txt.c

@@ -488,7 +488,6 @@ char * _lv_txt_set_text_vfmt(const char * fmt, va_list ap)
     if(text == NULL) {
         return NULL;
     }
-    text[len] = 0; /*Ensure NULL termination*/
 
     lv_vsnprintf(text, len + 1, fmt, ap);
 #endif