xz: Fix a crash in progress indicator when in passthru mode.

"xz -dcfv not_an_xz_file" crashed (all four options are
required to trigger it). It caused xz to call
lzma_get_progress(&strm, ...) when no coder was initialized
in strm. In this situation strm.internal is NULL which leads
to a crash in lzma_get_progress().

The bug was introduced when xz started using lzma_get_progress()
to get progress info for multi-threaded compression, so the
bug is present in versions 5.1.3alpha and higher.

Thanks to Filip Palian <Filip.Palian@pjwstk.edu.pl> for
the bug report.
3 files changed