Fix #81092: fflush before stream_filter_remove corrupts stream

When doing a non finishing flush, BZ2_bzCompress() returns BZ_FLUSH_OK
(not BZ_FINISH_OK) what requires us to do further fl

Fix #81092: fflush before stream_filter_remove corrupts stream

When doing a non finishing flush, BZ2_bzCompress() returns BZ_FLUSH_OK
(not BZ_FINISH_OK) what requires us to do further flushes right away.

We also refactor the while-loop as do-loop.

Closes GH-7113.

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