CGRect PSPDFRectSafeInset(CGRect rect, CGFloat dx, CGFloat dy) {
    CGRect insetRect = CGRectInset(rect, dx, dy);
    if (CGRectIsNull(insetRect)) {
        insetRect = CGRectMake(CGRectGetMidX(rect), CGRectGetMidY(rect), 0.f, 0.f);
    }
    return insetRect;
}