add-cluster: fix, stop handling dbl-click
add-cluster: fix, stop handling dbl-click

At the end of _user_mark_moles, stop handling double clicks. Otherwise
the user will be able to double-click later in the program to add more
moles and display them on the screen.

Test Plan:
Double-click the window when reviewing the montage, the display is
unchanged as expected.

aevri/mel,aevri/mel