Merge pull request #156 from ParsePlatform/richardross.query.crash.fix

Fixed rare crash in PFQuery related to weakify/strongify.

Author: richardjrossiii

Parse/PFQuery.m

@@ -842,6 +842,9 @@ - (BFTask *)_findObjectsAsyncForQueryState:(PFQueryState *)queryState after:(BFT
                                                                         user:user];
     }] continueWithBlock:^id(BFTask *task) {
         @strongify(self);
+        if (!self) {
+            return task;
+        }
         @synchronized (self) {
             if (_cancellationTokenSource == cancellationTokenSource) {
                 _cancellationTokenSource = nil;