Catch a possible NULL pointer deref in case the offsets got mangled somehow. As a consequence we may now get an unexpected result(*). Catch that error cases with a well defined panic giving appropriate pointers to ease debugging.
Catch a possible NULL pointer deref in case the offsets got mangled
somehow.
As a consequence we may now get an unexpected result(*).
Catch that error cases with a well defined panic giving appropriate
pointers to ease debugging.

(*) While the concensus was that the case should never happen unless
    there was a bug, noone was definitively sure.

Discussed with:		kmacy (about 8 months back)
Reviewed by:		silby (as part of a larger patch in March)
MFC after:		2 months

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