xfs_repair: Check if agno is inside the filesystem

xfs_repair: Check if agno is inside the filesystem

When getting an inode tree pointer from an array inode_tree_ptrs, we
should check if agno, which is used as a pointer to the array, lives
within the file system, because if it is not, we can end up touching
uninitialized memory. This may happen if we have corrupted directory
entry.

This commit fixes it by passing xfs_mount to affected functions and
checking if agno really is inside the file system.

This solves Red Hat bug #694706

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Alex Elder <aelder@sgi.com>