segfault on 'Run All Chunks' w/Rcpp chunk that fails compilation

[kevinushey]

Given this document:

```{Rcpp}
std::string x = 1;
```

```{r}
print(1)
```

If you try executing Run All, the IDE gets into a weird state where the Notebook execution engine believes that the following R chunks is ready and waiting to be executed. Attempting to do other stuff in the Notebook eventually triggers a segfault.

(repro'ed on macOS Desktop, v1.1.383)

[jmcphers]

I think there's an issue wherein certain kinds of errors can cause the chunk execution to abort, but in such a way that the cleanup doesn't happen. I'll take a look.

[jmcphers]

Backported to 1.1 here: 25f09e7

[dfalty]

Verified fixed 1.1.393.