Fix format-security error

[xiaoxiangmoe]

In macOS clang version 19.1.5

/Vanilla-Conquer/tiberiandawn/netdlg.cpp:4079:27: error: format string is not a string literal (potentially insecure) [-Werror,-Wformat-security]
 4079 |             sprintf(buf1, Text_String(TXT_WAITING_FOR_CONNECTIONS));
      |                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Vanilla-Conquer/tiberiandawn/netdlg.cpp:4079:27: note: treat the string as an argument to avoid this
 4079 |             sprintf(buf1, Text_String(TXT_WAITING_FOR_CONNECTIONS));
      |                           ^
      |                           "%s",