patch 8.2.1521: reading past end of buffer when reading spellfile

Problem:    Reading past end of buffer when reading spellfile. (Yegappan
            Lakshmanan)
Solution:   Store the byte length and check for it.
diff --git a/src/version.c b/src/version.c
index 41e9188..4560103 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1521,
+/**/
     1520,
 /**/
     1519,