MOHAWK: Reset some Myst state variables as per the original

This fixes a bug where the player could be stuck on Channelwood's
lower level with the elevator on the upper level.

This also turns the light off on Stoneship when entering the age,
since the battery is depleted.

Thanks to dtungsten for submitting this fix in PR#478.

engines/mohawk/myst_stacks/stoneship.cpp

@@ -42,6 +42,7 @@ Stoneship::Stoneship(MohawkEngine_Myst *vm) :
 
 	_tunnelRunning = false;
 
+	_state.lightState = 0;
 	_state.generatorDepletionTime = 0;
 	_state.generatorDuration = 0;
 	_cabinMystBookPresent = 0;

engines/mohawk/myst_state.cpp

@@ -100,6 +100,9 @@ bool MystGameState::load(const Common::String &filename) {
 	syncGameState(s, size == 664);
 	delete loadFile;
 
+	// Set Channelwood elevator state to down, because we start on the lower level
+	_channelwood.elevatorState = 0;
+
 	// Switch us back to the intro stack, to the linking book
 	_vm->changeToStack(kIntroStack, 5, 0, 0);