The order of function calls in an arithmetic expression is undefined and so
they must be written out as sequential statements.
Thanks to @dv-extrarius for reporting this issue, see issue #3690.
Adds check that LZ offsets fall into the sliding dictionary used. This
catches a case when uzlib.DecompIO with a smaller dictionary is used
to decompress data which was compressed with a larger dictionary.
Previously, this would lead to producing invalid data or crash, now
an exception will be thrown.
