patch 8.1.2210: using negative offset for popup_create() does not work

Problem:    Using negative offset for popup_create() does not work.
Solution:   Use -1 instead of zero. (closes #5111)
diff --git a/src/version.c b/src/version.c
index 728fa47..0347a68 100644
--- a/src/version.c
+++ b/src/version.c
@@ -742,6 +742,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2210,
+/**/
     2209,
 /**/
     2208,