In an unusual malpractice case against an expert witness who allegedly misdiagnosed the plaintiff in a prior malpractice case, Philip W. Sandler sued Jerry J. Sweet, Ph.D. — a clinical psychologist and neuropsychologist who was retained as a defense expert when Sandler sued Downers Grove-based Advocate Good Samaritan Hospital.Sandler asserted Sweet failed to correctly diagnose the extent of the brain injury he allegedly suffered because of Advocate’s negligence.Affirming a judgment that dismissed the complaint …