MT#55283 fix zero string length after copy

Big yikes.

Closes #1878

Change-Id: Id2d2a337a145b8fbf2a515154bf009a085300904
(cherry picked from commit b805252b94)

daemon/control_ng.c

@@ -446,6 +446,7 @@ static str dummy_encode_len(char *out, const char *in, size_t in_len) {
 static str *dummy_decode_len(const char *in, size_t len) {
 	str *r = str_alloc(len);
 	memcpy(r->s, in, len);
+	r->len = len;
 	r->s[len] = '\0';
 	return r;
 }