Add a function for creating an empty email address object.

* include/mailutils/address.h (mu_address_create_null): New proto.
* libmailutils/address/address.c (mu_address_create_null): New function.

@@ -62,6 +62,8 @@ struct mu_address
   struct mu_address *next;
 };
 
+extern int mu_address_create_null (mu_address_t *);
+  
 extern int mu_address_create_hint (mu_address_t *, const char *,
 				   mu_address_t, int);
   

@@ -36,6 +36,16 @@
 #include <mailutils/address.h>
 #include <mailutils/cstr.h>
 
+int
+mu_address_create_null (mu_address_t *pa)
+{
+  mu_address_t a = calloc (1, sizeof (*a));
+  if (!a)
+    return ENOMEM;
+  *pa = a;
+  return 0;
+}
+
 /* Get email addresses from rfc822 address.  */
 int
 mu_address_create_hint (mu_address_t *a, const char *s, mu_address_t hint,