perf: Speed up getNodeFromTree (#1302)

* fix: speed up getNodeFromTree

* remove return value for clear semantics

* fix early return nit

Author: paulirish

lib/core/utils/flattened-tree.js

@@ -142,15 +142,13 @@ axe.utils.getNodeFromTree = function(vNode, node) {
 		return vNode;
 	}
 	vNode.children.forEach(candidate => {
-		var retVal;
-
+		if (found) {
+			return;
+		}
 		if (candidate.actualNode === node) {
 			found = candidate;
 		} else {
-			retVal = axe.utils.getNodeFromTree(candidate, node);
-			if (retVal) {
-				found = retVal;
-			}
+			found = axe.utils.getNodeFromTree(candidate, node);
 		}
 	});
 	return found;