Merlin error when opening .ml file

Steps to reproduce:

```
git clone https://github.com/esy-ocaml/hello-reason.git
cd hello-reason
touch lib/A.ml
esy mvim lib/A.ml
```

Output:
```
"lib/A.ml" 0L, 0C
(merlin) backtrace:
Error detected while processing function merlin#Register[117]..merlin#LoadProject:
line 2:
Traceback (most recent call last):
File "", line 1, in
File "/Users/x/code/VimBox/dotVim/bundle/vim-reason/autoload/merlin.py", line 740, in setup_merlin
failures = command("project","get")
File "/Users/x/code/VimBox/dotVim/bundle/vim-reason/autoload/merlin.py", line 201, in command
return merlin_process().command(context(cmd))
File "/Users/x/code/VimBox/dotVim/bundle/vim-reason/autoload/merlin.py", line 170, in command
raise MerlinException(value)
merlin.MerlinException: 'File "src/kernel/mocaml.ml", line 29, characters 2-8: Assertion failed'
Press ENTER or type command to continue
```

I'm not sure if the error is with VimBox specifically.

Reproduce the failure with the hello-reason clone and the listed esy mvim command. Start in autoload/merlin.py at setup_merlin and command, then inspect src/kernel/mocaml.ml around line 29 to determine whether VimBox or Merlin triggers the assertion. Done means the source of the failure is identified and a verified resolution or clear project-side diagnosis is recorded.

Written by the indexing model from the issue text.