Do not display error while waiting for RESTful interface

When loading a large DOL file (or one with many imports), Hets-IDE needs some time to show the development graph. During this time, at the footer I get "Fetching graph for ..." (which is useful), but in the window on the right, I get
```
No file loaded!
Please close this pane and run the command again.
```
which does not make sense.


