e2fsck: Fix an unhandled corruption case in scan_extent_node()

A corrupted interior node in an extent tree would cause e2fsck to
crash with the error message:

Error1: Corrupt extent header on inode 107192
Aborted (core dumped)

Handle this and related failures when scanning an inode's extent tree
more robustly.

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