qjson: Improve debugging

Add an assert() to qobject_from_jsonf() to assure that the returned
QObject is not NULL. Currently this is duplicated in the callers.
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

qjson.c

@@ -53,6 +53,10 @@ QObject *qobject_from_json(const char *string)
     return qobject_from_jsonv(string, NULL);
 }
 
+/*
+ * IMPORTANT: This function aborts on error, thus it must not
+ * be used with untrusted arguments.
+ */
 QObject *qobject_from_jsonf(const char *string, ...)
 {
     QObject *obj;
@@ -62,6 +66,7 @@ QObject *qobject_from_jsonf(const char *string, ...)
     obj = qobject_from_jsonv(string, &ap);
     va_end(ap);
 
+    assert(obj != NULL);
     return obj;
 }