check tty in can_set_perm_invent

During very early startup, Windows may not have loaded
the tty window procs yet, and it is running with safeprocs.
It will eventually load the tty stuff. If the currently
operating window port fails in can_set_perm_invent(),
try the check for WC_PERM_INVENT again explicitly on
the tty windowport.

include/extern.h

@@ -3410,6 +3410,10 @@ extern void choose_windows(const char *);
 void addto_windowchain(const char *s);
 void commit_windowchain(void);
 #endif
+#ifdef TTY_GRAPHICS
+extern boolean check_tty_wincap(unsigned long);
+extern boolean check_tty_wincap2(unsigned long);
+#endif
 extern boolean genl_can_suspend_no(void);
 extern boolean genl_can_suspend_yes(void);
 extern char genl_message_menu(char, int, const char *);