Split RangeDecoder into RangeDecoderFromBuffer and FromStream.

To support LZMA1, support for reading from an InputStream is
needed. LZMA1-specific features are in FromStream while
LZMA2-specific features are in FromBuffer.

Move the rc.isInBufferOK() from LZMADecoder to LZMA2InputStream
since that is a LZMA2-specific thing.
6 files changed