libext2fs: Don't make a copy of the inode in ext2fs_extent_open2()

libext2fs: Don't make a copy of the inode in ext2fs_extent_open2()

Previously, ext2fs_extent_open2() copied the passed-in inode structure
into the extent handle, and the extent functions modified the copy of
the inode structure if necessary due to extent splits, etc.  Change
ext2fs_extent_open2() so that the extent functions use the inode
structure passed into ext2fs_extent_open2().  Otherwise the passed-in
inode structure could become out of date due to changes made by the
extent functions.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>