fix: Stop indexOf override from crashing Axe (#968)

Author: zkf

lib/core/utils/aggregateChecks.js

@@ -23,7 +23,7 @@ axe.utils.aggregateChecks = function (nodeResOriginal) {
 
 	// map each result value to a priority
 	anyAllNone(nodeResult, function (check, type) {
-		let i = checkMap.indexOf(check.result);
+		let i = typeof check.result === 'undefined' ? -1 : checkMap.indexOf(check.result);
 		// default to cantTell
 		check.priority = i !== -1 ? i : axe.constants.CANTTELL_PRIO;
 
@@ -72,4 +72,4 @@ axe.utils.aggregateChecks = function (nodeResOriginal) {
 	delete nodeResult.priority;
 
 	return nodeResult;
-};
+};