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.

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1521,
 /**/
     1520,
 /**/