Missing checks when updating an asset's bitasset_data

[abitmore]

When creating an asset, there are checks:

bitshares-core/libraries/chain/asset_evaluator.cpp

Lines 108 to 115 in 0054ce3

	FC_ASSERT( op.bitasset_opts->feed_lifetime_sec > chain_parameters.block_interval &&
	op.bitasset_opts->force_settlement_delay_sec > chain_parameters.block_interval );
	}
	if( op.is_prediction_market )
	{
	FC_ASSERT( op.bitasset_opts );
	FC_ASSERT( op.precision == op.bitasset_opts->short_backing_asset(d).precision );
	}

These are missing when updating.

[abitmore]

Fixed with #932.