Sync libdvdnav up to R1251.

* Fix failed assertion when there's no menu.
* Make sure we get nav packets for all cells in multi angle features
* Fix strict aliasing warnings.

Signed-off-by: Stuart Morgan <smorgan@mythtv.org>
Sync libdvdread to R1250:

* Accommodate duplicate language units and pgcs (avoid potentially consuming large amounts of memory)
* Fix a segmentation fault by preventing a read/write beyond end of an array due to using a length value taken from the DVD, which can exceed the allocated size.

Signed-off-by: Stuart Morgan <smorgan@mythtv.org>