If I remember correctly,the Glock is striker fired,no hammer,therefore no need to uncock it.
As far as being striker fired is concerned, you are correct. There is no hammer. However the factory instructions as well as all the other source instructions are clear. To break the Glock down you must pull the trigger all the way through first. It has something to do with positioning the transfer parts to a neutral position.
Since I have used a Glock for more than 2 decades (it was one of the 3 authorized semi autos by the Department) I am more than familiar with it's operation. It makes no difference to caliber, or generation, they ALL break down the same way.
It was also hammered into me on this and EVERY other weapon, during handling the FIRST thing you do is insure it is not loaded. The action is opened and cleared. I make myself do this 3 times with the Glock and still insure it's pointed in a safe direction before engaging the booger hook on the trigger.
Complacency and comfort with any type of machine is the first step to having an accident with it. Tools will bite and they have neither conscience nor regrets.