SizeSSZ panic when struct has nil pointer

[prestonvanloon]

Cannot Marshal / SizeSSZ when a struct has a nil pointer.

For example, if BeaconBlock.Body is nil, this will panic.

// SizeSSZ returns the ssz encoded size in bytes for the BeaconBlock object
func (b *BeaconBlock) SizeSSZ() (size int) {
        size = 76

        // Field (3) 'Body'
        size += b.Body.SizeSSZ()

        return
}

Using commit f7a73f0

[prestonvanloon]

Branch safe-check-nil-structs has a fix for this.