Auth0->exchange(): optimize redundant setcookie() calls (#591)

Co-authored-by: Evan Sims <[email protected]>

Author: Nebual

src/Auth0.php

@@ -309,15 +309,14 @@ public function exchange(
         $codeVerifier = null;
         $user = null;
 
+        $this->clear(false);
         $this->deferStateSaving();
 
         if ($code === null) {
             $this->clear();
             throw \Auth0\SDK\Exception\StateException::missingCode();
         }
 
-        $this->clear(false);
-
         if ($state === null || ! $this->getTransientStore()->verify('state', $state)) {
             $this->clear();
             throw \Auth0\SDK\Exception\StateException::invalidState();