fsharp-mode cannot displays type signatures and tooltips for input fsx files

### Description

fsharp-mode cannot displays type signatures and tooltips for input fsx files. also fsharp interactive and run through sfsharp seems to not work. it is possibly connected

### Repro steps

Please provide the steps required to reproduce the problem

1. open an .fsx file in emacs causing to it go into f sharp mode

2. highlight symbol in code

### Expected behavior

fsharp mode should display type signature in the minibuffer

### Actual behavior

instead the minibuffer displays File 'c:\path\file' not parsed

### Known workarounds

none

### Related information

* Operating system
windows 7

* Branch
* Emacs version
25.3
* .NET Runtime, CoreCLR or Mono Version
mono version 5.10.0.140
* Performance information, links to performance testing scripts

[debug.txt](https://github.com/fsharp/emacs-fsharp-mode/files/1868372/debug.txt)