Returns non-zero if the supplied ENGINE has a ctrl() handler. If "not", then
all the remaining control commands will return failure, so it is worth
checking this first if the caller is trying to "discover" the engine's
capabilities and doesn't want errors generated unnecessarily.
Returns non-zero if the supplied ENGINE has a ctrl() handler. If "not", then all the remaining control commands will return failure, so it is worth checking this first if the caller is trying to "discover" the engine's capabilities and doesn't want errors generated unnecessarily.