Some messages of the crystal compiler are not tied to a file.
This causes a 'Key not present in Dictionnary' error (E716).
For the record, the json output on ```require "./nonexistent.cr"```
is the following :
```json
[
{ "file":"/tmp/file.cr", "line":1, "column":1, "size":0,
"message":"while requiring \"./nonexistent.cr\"" },
{ "message":"can't find file './nonexistent.cr' relative to '/tmp'" }
]
```
The second message does not have line/column attributes.
