No pistol is truly safe to be carried loose in a pocket. Ask the guy who shot himself trying to draw his Glock, that had turned in the pocket. Or the guy that gave himself a .38 caliber vasectomy in an OKC food court try to ease the revolver out without being seen.
If anything, the Glock is slightly more dangerous being carried loose because the trigger pull is lighter than a revolver. Same reason that Glocks should never be carried in a holster that has an attached strap, like a revolver holster. Men have shot themselves in the leg when the strap somehow got in the Glock trigger guard when reholstering.
If I sound like a cranky old range safety officer, I am, and have seen many instances of "I don't know how that happened, I've been doing it that way for years." Industrial safety publications say unsafe acts are typically repeated on average 300 times with zero problems before they show up on an incident report.
A good pocket holster that covers the trigger is a wise investment, and greatly reduces risk. I don't own a Glock, but I use a S&W in a pocket holster.

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