Isal

+ Fix an error that occurred in the ``__close__`` function when a threaded
writer was initialized with incorrect parameters.

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+ Fix a bug where streams that were passed to igzip_threaded.open where closed.

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+ Fix a bug where compression levels for IGzipFile where checked in read mode.

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+ Fix a bug where append mode would not work when using
``igzip_threaded.open``.

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+ Fix a bug where a filehandle remained opened when ``igzip_threaded.open``
was used for writing with a wrong compression level.
+ Fix a memory leak that occurred when an error was thrown for a gzip header
with the wrong magic numbers.
+ Fix a memory leak that occurred when isal_zlib.decompressobj was given a
wrong wbits value.

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+ Fix a memory leak in the GzipReader.readall implementation.