patch 9.1.1016: Not possible to convert string2blob and blob2string

Problem:  Not possible to convert string2blob and blob2string
Solution: add support for the blob2str() and str2blob() functions

closes: #16373

Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/proto/mbyte.pro b/src/proto/mbyte.pro
index bb976e3..7061bab 100644
--- a/src/proto/mbyte.pro
+++ b/src/proto/mbyte.pro
@@ -31,6 +31,7 @@
 int utfc_char2bytes(int off, char_u *buf);
 int utf_ptr2len(char_u *p);
 int utf_byte2len(int b);
+int utf_byte2len_zero(int b);
 int utf_ptr2len_len(char_u *p, int size);
 int utfc_ptr2len(char_u *p);
 int utfc_ptr2len_len(char_u *p, int size);