Checking if object has defined key for Pointer constraints in liveQuery

[simonas-notcat]

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)

[codecov-io]

Current coverage is 92.87%

Merging #1487 into master will increase coverage by +0.01% as of 5f0a6e5

@@            master   #1487   diff @@
======================================
  Files           87      87       
  Stmts         5491    5491       
  Branches      1015    1015       
  Methods          0       0       
======================================
+ Hit           5099    5100     +1
  Partial         10      10       
+ Missed         382     381     -1

Review entire Coverage Diff as of 5f0a6e5

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[flovilmart]

@simonas-notcat weren't 2 of the 3 commits already merged?

[facebook-github-bot]

@simonas-notcat updated the pull request.