patch 8.2.4880: Vim9: misplaced elseif causes invalid memory access

Problem:    Vim9: misplaced elseif causes invalid memory access.
Solution:   Check cs_idx not to be negative.
diff --git a/src/version.c b/src/version.c
index 5a597a8..848c3e6 100644
--- a/src/version.c
+++ b/src/version.c
@@ -747,6 +747,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4880,
+/**/
     4879,
 /**/
     4878,