scope: crash on refreshing "Locals"

[lpaulsen93]

The following sequence of actions crashes Geany:

1. start debugging a program with the scope plugin
2. wait for a breakpoint
3. in the message window select "Debug" and then select tab "Locals"
4. right click inside the tab to show the context menu, select "Refresh"
5. Geany crashes (not always but often)

Remark: the crash does not occur if the user first left clicks into the "Locals" tab content area before selecting "Refresh".