When installing locking hardware on glass patio doors, it is necessary to drill directly toward the glass in order to make mounting holes. The glass will shatter or even explode even if only grazed by a spinning drill bit (I know, I've had to replace a patio glass door before and it's not cheap), let alone punctured by one.

Drill bit depth limiters are available at most hardware stores and are worth their weight in gold (and then some, as they hardly weigh anything). I advise you use them whenever you are drilling toward glass. They are collars with set screws that slide over your drill bit, and can be adjusted to limit the amount of bit exposed. They usually come in sets of 5 or 6 for varying drill bit sizes. Adjust the limiter so that only about 1/8" of bit protrudes beyond the tightened collar. If you don't have a set of these, you can cut plastic or rubber tubing to the appropriate length for the bit that you are using. Make certain you select tubing that is rigid enough to resist collapsing when pressure is applied.