patch 9.0.1688: cannot store custom data in quickfix list

Problem: cannot store custom data in quickfix list
Solution: add `user_data` field for the quickfix list

closes: #11818

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Tom Praschan <13141438+tom-anders@users.noreply.github.com>
diff --git a/src/version.c b/src/version.c
index dc054df..99f0013 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1688,
+/**/
     1687,
 /**/
     1686,