Win32: fix an incorrect error status being propagated to the caller in case where we fail to stat the destination path while being in the middle of a failed rename.
So, if we fail to stat the destination in the middle of such rename, propagate the *original* error. Because overriding the original error with the new one loses information about the actual cause of failure and may even confuse some of the callers, who for instance attempt to recover in case of an EACCES, since they may not be receiving that error at all.
(This is the behavior we had for a long time, even before r1865518, but now seems to be an appropriate moment to fix that)
* subversion/libsvn_subr/io.c (win32_file_rename): Use a separate `stat_err` for the case of the failed GetFileAttributes() call. If we failed to stat the file, return the original `err` status to the caller.