LiveQuery constrains matching fix (parse-community#2357)

* Removing sessionToken and authData from _User objects included in a query

This bug caused sessionToken to be replaced on client side to some old
sessionToken from DB.

* Removing dangling variable that is never used

* Checking if object has defined key for Pointer constraints in liveQuery

If there is a liveQuery subscription, with Pointer type constrains (e.g
query.equalTo('user', Parse.User.current())), and new object has
undefined value for that field, we get this error:

    error: Uncaught internal server error. [TypeError: Cannot read
property 'className' of undefined] TypeError: Cannot read property
'className' of undefined
    at matchesKeyConstraints
(…/node_modules/parse-server/lib/LiveQuery/QueryTools.js:145:51)

* LiveQuery constrains matching fix

When constrains == null, we get “Uncaught internal server error”

src/LiveQuery/QueryTools.js

@@ -117,6 +117,9 @@ function matchesQuery(object: any, query: any): boolean {
  * Determines whether an object matches a single key's constraints
  */
 function matchesKeyConstraints(object, key, constraints) {
+  if (constraints === null) {
+    return false;
+  }
   var i;
   if (key === '$or') {
     for (i = 0; i < constraints.length; i++) {