fuse: Add bad inode check in fuse_destroy_inode()

fuse: Add bad inode check in fuse_destroy_inode()

make_bad_inode() sets inode->i_mode to S_IFREG if I/O error is detected
in fuse_do_getattr()/fuse_do_setattr(). If the inode is not a regular
file, write_files and queued_writes in fuse_inode are not initialized
and have NULL or invalid pointers written by other members in a union.
So, list_empty() returns false in fuse_destroy_inode(). Add
is_bad_inode() to check if make_bad_inode() was called.

Reported-by: [email protected]
Fixes: ab2257e9941b ("fuse: reduce size of struct fuse_inode")
Signed-off-by: Myungho Jung <[email protected]>
Signed-off-by: Miklos Szeredi <[email protected]>