python/tarfile.cc: LFS: Handle too large file

Handle both file sizes larger than SIZE_MAX and allocation
failures when reading the data of a tarmember.

If using the go() function with a callback, pass None as the data
parameter for files that are too large. For extractdata, raise
a MemoryError if the file too extract is too large.

Also check for an existing error first in extractdata, before
raising a new one.

Test the whole thing on 32-bit platforms with a sample deb that
contains a zeroed file that is 5GB large (compressed using xz
at level 1 to a few kb).

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