Clicking loop end before loop begin makes the program crash

[Cheng-Hsiung]

When running manual loop closing, if loop end is (mis)clicked before loop begin was set, the program will crash with segmentation fault. The same error happens for plane-based correction: click loop end without loop begin -> sub window still appears -> click "add edge" then crashes.

error message: [1] 6819 segmentation fault (core dumped) rosrun interactive_slam interactive_slam

[koide3]

I just merged your PR. Thanks for your contribution 👍

[Cheng-Hsiung]

Glad it works, thanks.