patch 8.1.0643: computing byte offset wrong

Problem:    Computing byte offset wrong. (Bjorn Linse)
Solution:   Use the right variable for array index.
diff --git a/src/version.c b/src/version.c
index dc11358..06f7a8a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -800,6 +800,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    643,
+/**/
     642,
 /**/
     641,