SCI: Make -propDict- unique for each class

Previously, this was using the offset of the property dict inside the
script. However, this isn't unique. For example, SQ6's DPath and
PolyPath classes both have their property dict at offset 8 of their
respective scripts. This would break Obj::isMemberOf.

Closes #846.

engines/sci/engine/script.cpp

@@ -1058,11 +1058,17 @@ void Script::initializeObjectsSci11(SegManager *segMan, SegmentId segmentId) {
 		obj->setSuperClassSelector(
 			segMan->getClassAddress(obj->getSuperClassSelector().getOffset(), SCRIPT_GET_LOCK, 0));
 
-		// If object is instance, get -propDict- from class and set it for this
-		// object. This is needed for ::isMemberOf() to work.
+		// -propDict- is used by Obj::isMemberOf to determine if an object
+		// is an instance of a class. For classes, we therefore relocate
+		// -propDict- to the script's segment. For instances, we copy
+		// -propDict- from its class.
 		// Example test case - room 381 of sq4cd - if isMemberOf() doesn't work,
-		// talk-clicks on the robot will act like clicking on ego
-		if (!obj->isClass()) {
+		// talk-clicks on the robot will act like clicking on ego.
+		if (obj->isClass()) {
+			reg_t propDict = obj->getPropDictSelector();
+			propDict.setSegment(segmentId);
+			obj->setPropDictSelector(propDict);
+		} else {
 			reg_t classObject = obj->getSuperClassSelector();
 			const Object *classObj = segMan->getObject(classObject);
 			obj->setPropDictSelector(classObj->getPropDictSelector());