xz: fix incorrect eof at the end of an lzip member. (#2027)

xz: fix incorrect eof at the end of an lzip member. (#2027)

xz filter returns incorrect eof if the end of an lzip member is at the
end of the read buffer (`state->stream.next_in`).
At next call of `xz_filter_read()`, following lzip members are never
read since `state->eof` is still flagged.
Fixes #2026.