fix warning: X enumeration values not handled in switch [-Wswitch-enum]
fix warning: X enumeration values not handled in switch [-Wswitch-enum]

Add default cases to opcode switches to assert that they should never
occur.

Signed-off-by: Giel van Schijndel <b1c1d8736f20db3fb6c1c66bb1455ed43909f0d8@mortis.eu>

wastholm/bitcoin,wastholm/bitcoin,wastholm/bitcoin,wastholm/bitcoin,wastholm/bitcoin,wastholm/bitcoin