If you have one chambered, that'd be bad, but bullets tend to just explode a bit in microwaves. I can't tell the model of Glock, but there's twixt 8 & 12 rounds in there. If they all went off same time, they'd have parts of a Glock left (probably most of the upper, but the lower is fucked), a ruined microwave, and possibly a single round through the back and whatever's behind the microwave.
Demo Ranch did this with a single 50 cal bullet. Messed up the microwave, but everything outside it was fine.