patch 8.2.3438: cannot manipulate blobs

Problem:    Cannot manipulate blobs.
Solution:   Add blob2list() and list2blob(). (Yegappan Lakshmanan,
            closes #8868)
diff --git a/src/proto/typval.pro b/src/proto/typval.pro
index e509e4d..d13a1ec 100644
--- a/src/proto/typval.pro
+++ b/src/proto/typval.pro
@@ -17,6 +17,7 @@
 int check_for_float_or_nr_arg(typval_T *args, int idx);
 int check_for_bool_arg(typval_T *args, int idx);
 int check_for_opt_bool_arg(typval_T *args, int idx);
+int check_for_blob_arg(typval_T *args, int idx);
 int check_for_list_arg(typval_T *args, int idx);
 int check_for_opt_list_arg(typval_T *args, int idx);
 int check_for_dict_arg(typval_T *args, int idx);