Fix crash in graph where you print the current node twice.

Thanks to cokesme for the bug report.

https://www.dropbox.com/s/qa58v3kpw1pri30/r2_testing.tar.gz?dl=0
1. r2 csaw[...].exe

2. aa

3. VV

4. V

5. tab to section .text 

6. q

7. V

8. crash