In a usual comprehensive insurance policy, if the windshield glass (front or rear) alone gets damaged without any accidental damage to the car, the replacement will be considered as an Own Damage claim.
In this case, the No Claim Bonus (NCB) will not be available for next year renewal of your car insurance.
If a windshield cover is added in your car insurance, in case of damage to windshield without any damage to your car, the replacement of the glass for the first time during the year will not be considered as an OD claim. The No Claim Bonus will be available without any reduction during your next renewal.