fix potential infinite looping of resolver

In case a pointer to itself was received, the resolver looped inifinitely
until the stack overflows.

Signed-off-by: Steffen Jaeckel <jaeckel-floss@eyet-services.de>

ChangeLog

@@ -1,4 +1,5 @@
 0.12.0
+	- Fix potential infinite loop in resolver (#200)
 	- Add code coverage support
 	- New API:
 		- xmpp_stanza_get_child_by_path()

src/resolver.c

@@ -321,6 +321,9 @@ static unsigned message_name_get(const unsigned char *buf,
             if (i >= buf_len)
                 return 0;
             pointer = (label_len & 0x3f) << 8 | buf[i++];
+            /* Prevent infinite looping */
+            if (pointer == buf_offset)
+                return 0;
             if (name != NULL && name_len >= name_max && name_max > 0) {
                 /* We have filled the name buffer. Don't pass it recursively. */
                 name[name_max - 1] = '\0';