patch 8.2.4523: when gvim is started maximized the 'window' option isn't set

Problem:    When gvim is started maximized the 'window' option isn't set
            properly. (Christian J. Robinson)
Solution:   Check if 'windows' was already set or not. (Ken Takata,
            closes #9904)
diff --git a/src/term.c b/src/term.c
index f131ebf..14a05de 100644
--- a/src/term.c
+++ b/src/term.c
@@ -3380,7 +3380,8 @@
     {
 	// If 'window' uses the whole screen, keep it using that.
 	// Don't change it when set with "-w size" on the command line.
-	if (p_window == old_Rows - 1 || (old_Rows == 0 && p_window == 0))
+	if (p_window == old_Rows - 1
+		    || (old_Rows == 0 && !option_was_set((char_u *)"window")))
 	    p_window = Rows - 1;
 	old_Rows = Rows;
 	shell_new_rows();	// update window sizes