Add window_columns() function to determine number of columns used for splitting window output

Replaces two open-coded versions of the same pattern.

include/window.h

@@ -37,6 +37,7 @@
 	Window	*BX_new_window			(struct ScreenStru *);
 	void	BX_delete_window			(Window *);
 	void	BX_add_to_invisible_list		(Window *);
+int window_columns(Window *window);
 	Window	*BX_add_to_window_list		(struct ScreenStru *, Window *);
 	void	BX_remove_from_window_from_screen	(Window *);
 	void	BX_recalculate_window_positions	(struct ScreenStru *);

source/functions.c

@@ -6308,12 +6308,9 @@ BUILT_IN_FUNCTION(function_numlines, input)
 	char *s = NULL;
 	if (input && *input)
 	{
-		int cols;
+		int cols = window_columns(current_window);
+
 		s = LOCAL_COPY(input);
-		if (current_window->screen)
-			cols = current_window->screen->co;
-		else
-			cols = current_window->columns;
 		for (lines = split_up_line(s, cols + 1); *lines; lines++)
 			count++;
 	}

source/screen.c

@@ -218,10 +218,7 @@ void BX_add_to_window(Window *window, const char *str)
 		display_standout(OFF);
 		display_bold(OFF);
 
-		if (window->screen)
-			cols = window->screen->co;
-		else
-			cols = window->columns;
+		cols = window_columns(window);
 
 		for (lines = split_up_line(str, cols/* + 1*/); *lines; lines++)
 		{

source/window.c

@@ -427,6 +427,18 @@ void BX_add_to_invisible_list(Window *window)
 	window->screen = NULL;
 }
 
+/* window_columns()
+ *
+ * Returns the number of columns in the window for wrapping output.  For
+ * visible windows, this is the number of columns on the screen; for
+ * invisible windows, this is the saved size the window had when it was last
+ * visible.
+ */
+int window_columns(Window *window)
+{
+	return window->screen ? window->screen->co : window->columns;
+}
+
 /*
  * add_to_window_list: This inserts the given window into the visible window
  * list (and thus adds it to the displayed windows on the screen).  The