Get a filter instance identified by instance name from graph.
@param graph filter graph to search through.
@param name filter instance name (should be unique in the graph).
@return the pointer to the found filter instance or NULL if it
cannot be found.
Get a filter instance identified by instance name from graph.
@param graph filter graph to search through. @param name filter instance name (should be unique in the graph). @return the pointer to the found filter instance or NULL if it cannot be found.