Fix some behavioral regressions introduced by previous commit.

- Some parts of Tracker were basing certain assumptions on whether the
  types list was NULL or not. We now check on list emptiness instead.

src/kits/tracker/Model.cpp

@@ -1109,12 +1109,14 @@ Model::SupportsMimeType(const char* type, const BObjectList<BString>* list,
 		if (type) {
 			BString typeString(type);
 			match = MatchMimeTypeString(&typeString, mimeSignature);
-		} else
-			match = WhileEachListItem(const_cast<BObjectList<BString>*>(list),
-				MatchMimeTypeString, mimeSignature);
-				// const_cast shouldnt be here, have to have it until
-				// MW cleans up
-
+		} else {
+			if (list != NULL && !list->IsEmpty()) {
+				match = WhileEachListItem(const_cast<BObjectList<BString>*>(list),
+					MatchMimeTypeString, mimeSignature);
+			}
+			// const_cast shouldnt be here, have to have it until
+			// MW cleans up
+		}
 		if (match == kMatch)
 			// supports the actual type, it can't get any better
 			return kModelSupportsType;

src/kits/tracker/NavMenu.cpp

@@ -130,7 +130,7 @@ void
 SpringLoadedFolderSetMenuStates(const BMenu* menu,
 	const BObjectList<BString>* typeslist)
 {
-	if (!menu || !typeslist)
+	if (!menu || !typeslist || typeslist->IsEmpty())
 		return;
 
 	//	if a types list exists
@@ -339,13 +339,6 @@ BNavMenu::AttachedToWindow()
 void
 BNavMenu::DetachedFromWindow()
 {
-	//	does this need to set this to null?
-	//	the parent, handling dnd should set this
-	//	appropriately
-	//
-	//	if this changes, BeMenu and RecentsMenu
-	//	in Deskbar should also change
-	fTypesList = NULL;
 }
 
 
@@ -819,7 +812,10 @@ BNavMenu::SetShowParent(bool show)
 void
 BNavMenu::SetTypesList(const BObjectList<BString>* list)
 {
-	*fTypesList = *list;
+	if (list != NULL)
+		*fTypesList = *list;
+	else
+		fTypesList->MakeEmpty();
 }