patch 9.0.1617: charidx() result is not consistent with byteidx()

Problem:    charidx() and utf16idx() result is not consistent with byteidx().
Solution:   When the index is equal to the length of the text return the
            lenght of the text instead of -1. (Yegappan Lakshmanan,
            closes #12503)
diff --git a/src/version.c b/src/version.c
index e6858c2..a3fc959 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1617,
+/**/
     1616,
 /**/
     1615,