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/errors.h b/src/errors.h
index 2811a32..6bab826 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -3657,3 +3657,5 @@
 	INIT(= N_("E1513: Cannot switch buffer. 'winfixbuf' is enabled"));
 EXTERN char e_invalid_return_type_from_findfunc[]
 	INIT(= N_("E1514: 'findfunc' did not return a List type"));
+EXTERN char e_str_encoding_failed[]
+	INIT(= N_("E1515: Unable to convert %s '%s' encoding"));