Insurance — Professional liability — Duty to defend — Trial court erred in entering summary declaratory judgment finding that insurer had duty to defend insured where insurer raised affirmative defense that coverage had been extinguished through settlement of other claims — There is an exception to the general rule that the duty to defend is determined by looking only at the pleadings where the duty to defend turns on whether the policy limits have been exhausted — Affidavit filed by insurer created genuine issue of material fact as to whether policy limits were exhausted which precluded granting of insured’s motion for summary judgment