Yes
https://aimingexpert.com/will-a-glock-fire-without-a-magazine/
"Glocks will fire without a magazine present. The safety measure on a Glock is built into the trigger. If a round is chambered, regardless of whether a magazine is present, the firing pin will strike the percussion cap and a round will be fired when the trigger is pulled."
And actually, I hadn't thought of that. It would be easy to just drop the magazine, point the weapon out the window and shoot. It would also fit the evidence of where the items were found.
The photo I posted earlier was not how all the items were found. They were placed together for that photograph, but in actual fact the weapon and the spent cartridge were found in the back seat, the ring and magazine were found on the front passenger's seat.
If Walker was a righty, all he had to do was hold his hand to the right, and drop the magazine onto the passenger seat and then point the weapon out the window and shoot. The Glock 19 ejects the spent cartridge up, back and left, so from the driver's position, pointing it out the window (not putting the whole gun outside) and firing would eject the shell towards the rear seat
*
Of course, the slide locks back when the last round is fired, magazine or no magazine, but it will come forward with a flick of the slide lock, again, magazine, or no magazine.
*ETA: Also, shell casing was found on the road at the spot where the muzzle flash was recorded, but they haven't yet determined if it is a match to Walker's weapon.