Never pass NULL block pointer when reading. This is neither expected nor handled by lower layers like vdev_raidz, which uses bp for checksum verification. This bug could lead to NULL pointer reference and resets during boot.
Never pass NULL block pointer when reading. This is neither expected nor
handled by lower layers like vdev_raidz, which uses bp for checksum
verification. This bug could lead to NULL pointer reference and resets
during boot.

MFC after:	3 days

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