Fix ExtUI automatic font scaling (#18377)

Marlin/src/lcd/extui/lib/ftdi_eve_touch_ui/ftdi_eve_lib/extended/command_processor.h

       #ifdef TOUCH_UI_USE_UTF8
         const bool is_utf8 = has_utf8_chars(text);
       #endif
-      for (;font >= 26;) {
+      for (;font > 26;) {
         int16_t width, height;
         #ifdef TOUCH_UI_USE_UTF8
           if (is_utf8) {