json-streamer: Don't leak tokens on incomplete parse

Valgrind complained about a number of leaks in
tests/check-qobject-json:

==12657==    definitely lost: 17,247 bytes in 1,234 blocks

All of which had the same root cause: on an incomplete parse,
we were abandoning the token queue without cleaning up the
allocated data within each queue element.  Introduced in
commit 95385fe9, when we switched from QList (which recursively
frees contents) to g_queue (which does not).

We don't yet require glib 2.32 with its g_queue_free_full(),
so open-code it instead.

CC: qemu-stable@nongnu.org
Signed-off-by: NEric Blake <eblake@redhat.com>
Message-Id: <1463608012-12760-1-git-send-email-eblake@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
(cherry picked from commit ba4dba54)
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

qobject/json-streamer.c

@@ -20,9 +20,15 @@
 #define MAX_TOKEN_COUNT (2ULL << 20)
 #define MAX_NESTING (1ULL << 10)
 
+static void json_message_free_token(void *token, void *opaque)
+{
+    g_free(token);
+}
+
 static void json_message_free_tokens(JSONMessageParser *parser)
 {
     if (parser->tokens) {
+        g_queue_foreach(parser->tokens, json_message_free_token, NULL);
         g_queue_free(parser->tokens);
         parser->tokens = NULL;
     }