a #GstQuery
Pointer to a #guint into which to store the currently selected angle value from the query, or NULL
Pointer to a #guint into which to store the number of angles value from the query, or NULL
true if the query could be successfully parsed. false if not.
Parse the current angle number in the #GstNavigation angles query into the #guint pointed to by the cur_angle variable, and the number of available angles into the #guint pointed to by the n_angles variable.