make sure tableView:objectValueForTableColumn:row: doesn't fail even …

…if the data has already been released since the cleanup can trigger after enptying the data (PR#16561)

git-svn-id: https://svn.r-project.org/R-packages/trunk/Mac-GUI@7108 694ef91d-65df-0310-b7bb-92e67a308ead

REditor.m

@@ -476,10 +476,12 @@ - (void)tableViewSelectionIsChanging:(NSNotification *)aNotification
 
 - (id)tableView:(NSTableView *)tableView objectValueForTableColumn:(NSTableColumn *)tableColumn row:(NSInteger)row
 {
-
 	if(row < 0) return @"…";
-	return NSArrayObjectAtIndex(NSArrayObjectAtIndex(objectData, [[tableColumn identifier] intValue]), row);
-
+	int col = (int) [[tableColumn identifier] intValue];
+	if (col >= [objectData count]) return @"…";
+	NSArray *a = NSArrayObjectAtIndex(objectData, col);
+	if (!a || row >= [a count]) return @"…";
+	return NSArrayObjectAtIndex(a, row);
 }
 
 - (void)tableView:(NSTableView *)aTableView setObjectValue:(id)anObject forTableColumn:(NSTableColumn *)tableColumn row:(NSInteger)row