[CALC] When displaying "error", copying text misses last letter

reactos-bootcd-0.4.16-dev-12-gbad0dd5-x86-gcc-lin-dbg

• Open Calc
• SQRT(-1)
• Shows "Erreur" (French)
• Ctrl+C (or File > Copy)
• Paste shows "Erreu" (missing last "r")

Root cause : handle_copy_command should not "display[n - calc.sDecimal_len] = _T('\0')"  if calc.is_nan is true.

Guilty code : https://git.reactos.org/?p=reactos.git;a=blob;f=base/applications/calc/winmain.c;hb=7b081be46de966e3fe6c2aa47a5a26deb7541e8a#l1021