Trouble Loading Saved Profile Data

# Summary

Hello! Thanks for this package, I've had a great experience using it so far. The only small snag that I've hit is when trying to load saved data.

# Reproducing the problem
For example, if I have some profiling data saved in `_03_profile_data.jlprof` (saved using `save("_03_profile_data.jlprof", Profile.retrieve()...)`) and I try to load it into pprof like:

```
julia> data = load("_03_profile_data.jlprof")
julia> pprof(data[1], data[2])
```

It looks as if all profiling data is in an unknown call and I can't access any of the fine-grain information. But if I create a `flamegraph` first and then load that into `pprof`, everything seems to work fine.

```
julia> data = load("_03_profile_data.jlprof")
julia> g = flamegraph(data[1]; lidict=data[2])
julia> pprof(g)

```

# Next Steps
The second solution above is fine with me for now since it's only an extra line, but I feel like I'm not doing something correctly. Have I missed something here?

Thanks!