Handling `sysFatal` gracefully
Unhandled sysFatal from top level scope can crash the repl:

```
%zsh> inim
👑 INim 0.6.1
Nim Compiler Version 1.6.0 [Linux: amd64] at /usr/bin/nim
nim> var s = newSeq[int](5)
nim> s[5] = 42
fatal.nim(53)            sysFatal
Error: unhandled exception: value out of range: -1 notin 0 .. 9223372036854775807 [RangeDefect]
```

Other unhandled sysFatal don't show the error message:

```
%zsh> inim
👑 INim 0.6.1
Nim Compiler Version 1.6.0 [Linux: amd64] at /usr/bin/nim
nim> proc oof() =
....   var s = newSeq[int](5)
....   s[5] = 42
....
nim> oof()
/usr/lib/nim/lib/system/fatal.nim(53) sysFatal
```