bug: sometimes electron fiddle freezes when starting a fiddle

Not "frozen" in the total sense -- more, Electron Fiddle is still responding to user input, and _says_ the Fiddle is running, but nothing happens.

I'm not sure if it's related, but when opening up devtools during a 'frozen' run like this, the console is full of:

```
DevTools failed to load SourceMap: Could not parse content for file:///C:/Users/electron/AppData/Local/electron-fiddle/app-0.25.2/resources/app.asar/dist/static/mobxreact.cjs.production.min.js.map: Unexpected end of JSON input
2
DevTools failed to load SourceMap: Could not parse content for file:///C:/Users/electron/AppData/Local/electron-fiddle/app-0.25.2/resources/app.asar/dist/static/index.js.map: Unexpected end of JSON input
DevTools failed to load SourceMap: Could not parse content for file:///C:/Users/electron/AppData/Local/electron-fiddle/app-0.25.2/resources/app.asar/dist/static/classes.js.map: Unexpected end of JSON input
DevTools failed to load SourceMap: Could not parse content for file:///C:/Users/electron/AppData/Local/electron-fiddle/app-0.25.2/resources/app.asar/dist/static/itemListRenderer.js.map: Unexpected end of JSON input
DevTools failed to load SourceMap: Could not parse content for file:///C:/Users/electron/AppData/Local/electron-fiddle/app-0.25.2/resources/app.asar/dist/static/itemRenderer.js.map: Unexpected end of JSON input
DevTools failed to load SourceMap: Could not parse content for file:///C:/Users/electron/AppData/Local/electron-fiddle/app-0.25.2/resources/app.asar/dist/static/listItemsProps.js.map: Unexpected end of JSON input
DevTools failed to load SourceMap: Could not parse content for file:///C:/Users/electron/AppData/Local/electron-fiddle/app-0.25.2/resources/app.asar/dist/static/listItemsUtils.js.map: Unexpected end of JSON input
DevTools failed to load SourceMap: Could not parse content for file:///C:/Users/electron/AppData/Local/electron-fiddle/app-0.25.2/resources/app.asar/dist/static/predicate.js.map: Unexpected end of JSON input
DevTools failed to load SourceMap: Could not parse content for file:///C:/Users/electron/AppData/Local/electron-fiddle/app-0.25.2/resources/app.asar/dist/static/index.js.map: Unexpected end of JSON input
DevTools failed to load SourceMap: Could not parse content for file:///C:/Users/electron/AppData/Local/electron-fiddle/app-0.25.2/resources/app.asar/dist/static/omnibar.js.map: Unexpected end of JSON input
DevTools failed to load SourceMap: Could not parse content for file:///C:/Users/electron/AppData/Local/electron-fiddle/app-0.25.2/resources/app.asar/dist/static/queryList.js.map: Unexpected end of JSON input
DevTools failed to load SourceMap: Could not parse content for file:///C:/Users/electron/AppData/Local/electron-fiddle/app-0.25.2/resources/app.asar/dist/static/multiSelect.js.map: Unexpected end of JSON input
DevTools failed to load SourceMap: Could not parse content for file:///C:/Users/electron/AppData/Local/electron-fiddle/app-0.25.2/resources/app.asar/dist/static/select.js.map: Unexpected end of JSON input
DevTools failed to load SourceMap: Could not parse content for file:///C:/Users/electron/AppData/Local/electron-fiddle/app-0.25.2/resources/app.asar/dist/static/suggest.js.map: Unexpected end of JSON input
DevTools failed to load SourceMap: Could not parse content for file:///C:/Users/electron/AppData/Local/electron-fiddle/app-0.25.2/resources/app.asar/root.f39bf48d.css.map: Unexpected end of JSON input
```
Possibly there is a timing issue between code that needs asar and code that doesn't?