gtk2: DrawText implementation DT_NOPREFIX faulty handling

Original Reporter info from Mantis: AntonK

• Reporter name: Anton Kavalenka

Description:

TLabel with ShowAccelChar=true always cause GTK2 to complain in console:

project1:11848): Pango-[1;33mWARNING[0m **: Invalid UTF-8 string passed to pango_layout_set_text()

This happens only with cyrillic text prefixed with ampersand &

Steps to reproduce:

Run the attached project. GTK2 complains only on '&Привет' caption but not on '&__Привет'

Mantis conversion info:

• Mantis ID: 31674
• OS: Linux
• OS Build: Debian 9.0
• Platform: i386
• Version: 1.7 (SVN)
• Fixed in revision: r54633 (#ae6948b6)