Maintain the original inode value for renamed files.

In case two renames are done on the same file/folder very quickly we
lost the information that the second operation was also a rename. That
was because we tried to get the inode value from a stat on the file once
the first rename was finished. But at that point, the file was already
gone because of the second rename.

Now the original inode is kept and written to db in case the file can
not be stat'ed.

This fixes bug #1737