Added virtual dtor to OutBuffer

include/amqpcpp/outbuffer.h

@@ -38,6 +38,13 @@ protected:
     virtual void append(const void *data, size_t size) = 0;
 
 public:
+    /**
+     *  Destructor
+     */
+    virtual ~OutBuffer()
+    {
+    }
+
     /**
      *  Add a binary buffer to the buffer
      *  @param  string  char* to the string