Fixed another end boundary condition with non-segmented mp4 (CVP2RI-397)

Testing with time-range 179-180 of O-AVC_MP4_HP_HD-08.MP4 uncovered another
 end-time issue. In this case, 180s resolves to the very last sample in the
 mp4. The logic to detect this end-of-range condition, however, was using
 SampleSizeBox.last_sample_number() - which was returning entry_size_array
 .length+1 - which is not correct. This is now fixed to return the length.

Re-ran the test - and range tests against the above file,
 B-AVC_MP4_MP_SD-08.MP4, and O-AVCMP4_BC15A-02.mp4