I worked with laminated glass, plate glass / mirror and plastics for 30yrs until I became a disabled Vet. My experience tought me how to stop a 'run' in glass and lexan / plexi glass by drilling a tiny hole at the very end of the 'run', crack, so that when it continues to run, it will have to stop at the tiny drilled hole. Use the smallest drill bit you can find.
If you'd rather not test yourself by drilling a hole, you can hope it does not "run" any farther by just barely tightening that fastener where it's cracked putting least amount of pressure on that area.
EDIT:
Sorry for repeating what you said above Svt40.