Avoid layout when providing cell values (fixes #73)

-tableView:objectValueForTableColumn:row: may call -layoutCandidateView,
which in turn may force the table view to reload; the layout code
should only run after all cell values are provided for to break this
potential cycle.

Source/CandidateUI/VTVerticalCandidateController.m

@@ -338,6 +338,12 @@ static const CGFloat kCandidateTextLeftMargin = 8.0;
 }
                            
 - (void)layoutCandidateView
+{
+    [NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(deferredLayoutCandidateView) object:nil];
+    [self performSelector:@selector(deferredLayoutCandidateView) withObject:nil afterDelay:0.0];
+}
+
+- (void)deferredLayoutCandidateView
 {
     NSUInteger count = [_delegate candidateCountForController:self];
     if (!count) {