always keep x_cols and x_lins valid; check once at start including tty init

if we find any, but not later; do not check on every read

⇒ allows changing COLUMNS and LINES (independent of each other, or both)
  for script shells by passing them in an environment setting, even if
  we get a tty; interactive shells still check before each line is read…

reported by the PLD guys, thanks

main.c

@@ -34,7 +34,7 @@
 #include <locale.h>
 #endif
 
-__RCSID("$MirOS: src/bin/mksh/main.c,v 1.207 2012/03/23 19:38:12 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/main.c,v 1.208 2012/03/23 21:58:21 tg Exp $");
 
 extern char **environ;
 
@@ -258,6 +258,12 @@ main_init(int argc, const char *argv[], Source **sp, struct block **lp)
 
 	init_histvec();
 
+#ifdef TIOCGWINSZ
+	/* try to initialise tty size before importing environment */
+	tty_init(false, false);
+	change_winsz();
+#endif
+
 #ifdef _PATH_DEFPATH
 	def_path = _PATH_DEFPATH;
 #else