Facebook login issue #510

@Scott, @pupi1985

This fix is written and verified by http://question2answer.org/qa/user/Dan+D. in below thread http://question2answer.org/qa/56966/facebook-login-stopped-working-its-not-even-working-your-site?show=56992#a56992
also see https://github.com/q2a/question2answer/issues/510

I'm just submitting code changes.

Please check line no 593 for currentUrl. 

Thanks to Q2A user Dan D, and Github users valan, iamdand, cksagherian for this patch.

qa-plugin/facebook-login/base_facebook.php

@@ -372,18 +372,17 @@ abstract class BaseFacebook
       return false;
     }
 
-    $response_params = array();
-    parse_str($access_token_response, $response_params);
-
-    if (!isset($response_params['access_token'])) {
+    $response = json_decode($access_token_response);
+    if (!isset($response->access_token)) {
       return false;
     }
 
     $this->destroySession();
 
     $this->setPersistentData(
-      'access_token', $response_params['access_token']
+      'access_token', $response->access_token
     );
+    
   }
 
   /**
@@ -789,13 +788,12 @@ abstract class BaseFacebook
       return false;
     }
 
-    $response_params = array();
-    parse_str($access_token_response, $response_params);
-    if (!isset($response_params['access_token'])) {
+   $response = json_decode($access_token_response);
+    if (!isset($response->access_token)) {
       return false;
     }
+    return $response->access_token;
 
-    return $response_params['access_token'];
   }
 
   /**