Breakpoint state is not restored if cfviz throws an exception

[Botond Ballo]

Steps to reproduce:

1. Run gdb on a program without starting the program yet
2. Set a breakpoint
3. Run cfviz. It will throws an exception saying "The program is not being run." (that's fine).
4. Run info breakpoints. Observe that the breakpoint set in step #2 is disabled.

The problem is that the cleanup code that restores the breakpoints to their previous enabled/disabled state does not run if an exception is thrown.

[Botond Ballo]

Restore breakpoint state even if an exception occurs during navigation (fixes #32)

→ <<cset b139e3c93474>>