* Electron version: 1.6.3
* Operating system: Linux

### Expected behavior

When registering a `beforeunload` handler which cancels unloading, I would expect the handler to be called for every `BrowserWindow.reload()`.

### Actual behavior

On 1.6.3, the `beforeunload` handler is called for the first `reload` but not on subsequent calls. Even after removing the event handler, `reload` will not reload the window anymore.

### How to reproduce

```javascript
const cancelUnload = e => {
   console.log('cancelUnload called')
   e.returnValue = false
}

window.addEventListener('beforeunload', cancelUnload)

remote.getCurrentWindow().reload()  // [1] -> cancelUnload called
remote.getCurrentWindow().reload()  // [2] -> cancelUnload called

remote.getCurrentWindow().close()   // [3] -> cancelUnload called
remote.getCurrentWindow().close()   // [4] -> cancelUnload called

window.removeEventListener('beforeunload', cancelUnload)

remote.getCurrentWindow().reload()  // [5] -> reloads window

remote.getCurrentWindow().close()   // [6] -> closes window
```
I would expect `cancelUnload` to be printed to the console four times and the step at `[5]` to actually reload the window. This is works up to Electron 1.6.2.

On Electron 1.6.3 `cancelUnload` is not printed at step `[2]` (nor on any subsequent calls to reload). What's more, event after removing the `beforeunload` handler, `reload` does not work anymore: at step `[5]` the window does not reload (but closing the window at `[6]` works).
atom/browser/api/atom_api_web_contents.cc
content::NavigationHandle* navigation_handle) {
  bool is_main_frame = navigation_handle->IsInMainFrame();
  if (navigation_handle->HasCommitted() && !navigation_handle->IsErrorPage()) {
    auto url = navigation_handle->GetURL();
    bool is_in_page = navigation_handle->IsSamePage();
    if (is_main_frame && !is_in_page) {
      Emit("did-navigate", url);
    } else if (is_in_page) {
      Emit("did-navigate-in-page", url, is_main_frame);
    }
  } else {
    auto url = navigation_handle->GetURL();
    int code = navigation_handle->GetNetErrorCode();
    auto description = net::ErrorToShortString(code);
    Emit("did-fail-provisional-load", code, description, url, is_main_frame);
    
    if (code != net::ERR_ABORTED)
      Emit("did-fail-load", code, description, url, is_main_frame);
  }
}
void WebContents::TitleWasSet(content::NavigationEntry* entry,