Do not allow the user to tap the start sharing button twice quickly
Just disable the button after it has been clicked.
If the user denies the location permission and selects "don't ask me again", they will end up with the fragment that has a disabled button. I think given that they just denied that permission, that's OK. They can still close the activity and start it again.
When navigating back from the next activity, the button is activated without any action we need to take.