patch 8.1.2123: parsing CSI sequence is messy

Problem:    Parsing CSI sequence is messy.
Solution:   Generalize parsing a CSI sequence.
diff --git a/src/version.c b/src/version.c
index e207a37..f07d038 100644
--- a/src/version.c
+++ b/src/version.c
@@ -754,6 +754,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2123,
+/**/
     2122,
 /**/
     2121,