Queries should not specify a batchSize of zero by default

[jmikola]

The folks at ResearchGate are having an issue with find commands encountering errors from mongos due to the adapter defaulting the batchSize option to 0. Relevant code is:

• Alcaeus\MongoDbAdapter\AbstractCursor::$batchSize defaults to zero.
• Alcaeus\MongoDbAdapter\AbstractCursor::getOptions() returns that property because it is non-null.
• MongoCursor::doQuery() includes all cursor options when invoking MongoDB\Collection::find().

See this comment in SERVER-28019 for more information.

Is there a particular reason that Alcaeus\MongoDbAdapter\AbstractCursor::$batchSize defaults to zero? Would leaving the property uninitialized (i.e. null) break compatibility for ODM or other dependent libraries?