libext2fs: ext2fs_dup_handle should not alias MMP buffers

libext2fs: ext2fs_dup_handle should not alias MMP buffers

It turns out that resize2fs uses ext2fs_dup_handle to duplicate fs handles.  If
MMP is enabled, this causes both handles to share MMP buffers, which is bad
news when it comes time to free both handles.  Change the code to (we hope) fix
this.  This prevents resize2fs from failing with a double-free error when
handed a MMP filesystem.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>