lgetxattr(2) man page says:
> If size is specified as zero, these calls return the current size of
> the named extended attribute (and leave value unchanged). This can be
> used to determine the size of the buffer that should be supplied in a
> subsequent call. (But, bear in mind that there is a possibility that
> the attribute value may change between the two calls, so that it is
> still necessary to check the return status from the second call.)
The current code does not handle the case when the size changes between
the two calls, and the new size is larger.
Fix the above problem, and slightly simplify the code.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
669056f93d