* Pull _UnwriteLastPartialChunk() out of Reinit() for reuse.
* _UnwriteLastPartialChunk(): fPendingDataSize wasn't set.
* _PushChunks(): Some simplifications for clarity.
* ChunkBuffer/RemoveDataRanges(): Use data reading and decompression
methods provided by our base class instead of duplicating the
implementation.
* RemoveDataRanges():
- _FlushPendingData() before starting, so we don't ignore the pending
data and _UnwriteLastPartialChunk() when done, so a partial chunk
is read back into the pending data buffer.
- fUncompressedHeapSize wasn't reset before the main processing loop,
thus resulting in an erroneous size later on.
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