Returns the value indexed by the given key inside the given channel.
User defined pointers returned by this function were stored by calls to vortex_channel_set_data or vortex_channel_set_data_full.
|channel ||The channel where data will be looked up.|
|key ||The index key to use. Though the API expects an axlPointer, the hash storing values is configured to receive string keys.|
- the value or NULL if fails.