MOHAWK: Fix uninitialized memory accesses in the Myst stacks

engines/mohawk/myst_stacks/credits.cpp

@@ -37,6 +37,7 @@ namespace MystStacks {
 
 Credits::Credits(MohawkEngine_Myst *vm) : MystScriptParser(vm) {
 	setupOpcodes();
+	_curImage = 0;
 }
 
 Credits::~Credits() {

engines/mohawk/myst_stacks/mechanical.cpp

@@ -40,6 +40,9 @@ Mechanical::Mechanical(MohawkEngine_Myst *vm) :
 	setupOpcodes();
 
 	_elevatorGoingMiddle = false;
+	_elevatorPosition = 0;
+
+	_crystalLit = 0;
 
 	_mystStaircaseState = false;
 	_fortressPosition = 0;

engines/mohawk/myst_stacks/selenitic.cpp

@@ -41,6 +41,10 @@ Selenitic::Selenitic(MohawkEngine_Myst *vm) :
 	setupOpcodes();
 	_mazeRunnerPosition = 288;
 	_mazeRunnerDirection = 8;
+	_mazeRunnerDoorOpened = false;
+
+	_soundReceiverDirection = 0;
+	_soundReceiverStartTime = 0;
 }
 
 Selenitic::~Selenitic() {

engines/mohawk/myst_stacks/stoneship.cpp

@@ -50,6 +50,8 @@ Stoneship::Stoneship(MohawkEngine_Myst *vm) :
 	_chestDrawersOpen = 0;
 	_chestAchenarBottomDrawerClosed = 1;
 
+	_brotherDoorOpen = 0;
+
 	// Drop key
 	if (_state.trapdoorKeyState == 1)
 		_state.trapdoorKeyState = 2;