CDAP-984 fix long overflow bug that would cause stream events

to not get read.
The case that was failing tests was the following:

Live file has length 253. The last split for the file has offset 253 and length max long.  In this section, it seeks to position 253, but then calls readTimestamp() (which throws an eofException) before it can check the condition and break out of the loop.  Therefore the position gets set to position 233, and the same event is read in 2 splits.