Fix a major memory leak in CSBzip2Handle

[altimac]

while using XADMaster, I noticed huge memory usage for very tiny files (uncompressing a ~100 bytes bizp2 file leak about 3,5MB of memory!). I started by adding a unit test to prove that, and it effectively show a major leak in Instruments.

Then I fixed it pretty easily. Please accept this quite short PR

Here is attached a screenshot showing the leak after about 1000 tiny files uncompression.

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