patch 8.2.1687: Vim9: out of bounds error

Problem:    Vim9: out of bounds error.
Solution:   Check that cmdidx is not negative.
diff --git a/src/version.c b/src/version.c
index a0a6983..0d0eaa5 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1687,
+/**/
     1686,
 /**/
     1685,