patch 9.1.0147: Cannot keep a buffer focused in a window

Problem:  Cannot keep a buffer focused in a window
          (Amit Levy)
Solution: Add the 'winfixbuf' window-local option
          (Colin Kennedy)

fixes:  #6445
closes: #13903

Signed-off-by: Colin Kennedy <colinvfx@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/ex_cmds.c b/src/ex_cmds.c
index 720e918..a12d819 100644
--- a/src/ex_cmds.c
+++ b/src/ex_cmds.c
@@ -2428,6 +2428,9 @@
     int		retval;
     char_u	*free_me = NULL;
 
+    if (!check_can_set_curbuf_forceit(forceit))
+	return GETFILE_ERROR;
+
     if (text_locked())
 	return GETFILE_ERROR;
     if (curbuf_locked())