patch 9.1.0393: 'viewdir' not respecting $XDG_CONFIG_HOME

Problem:  'viewdir' not respecting $XDG_CONFIG_HOME
          (Danilo Rezende, after v9.1.327)
Solution: adjust 'viewdir' option when enabling XDG config mode

fixes: #14680
closes: #14708

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/option.c b/src/option.c
index 0cd2823..2acc0d4 100644
--- a/src/option.c
+++ b/src/option.c
@@ -417,6 +417,14 @@
     options[opt_idx].def_val[VI_DEFAULT] = xdg_rtp;
     p_pp = xdg_rtp;
 
+#if defined(XDG_VDIR) && defined(FEAT_SESSION)
+    if ((opt_idx = findoption((char_u *)"viewdir")) < 0)
+	goto theend;
+
+    options[opt_idx].def_val[VI_DEFAULT] = (char_u *)XDG_VDIR;
+    p_vdir = (char_u *)XDG_VDIR;
+#endif
+
 theend:
     vim_free(vimrc1);
     vim_free(vimrc2);