* 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
#include "atom/browser/api/atom_api_web_contents.h"
#include <set>
#include <string>
#include "atom/browser/api/atom_api_debugger.h"
#include "atom/browser/api/atom_api_session.h"
#include "atom/browser/api/atom_api_window.h"
#include "atom/browser/atom_browser_client.h"
#include "atom/browser/atom_browser_context.h"
#include "atom/browser/atom_browser_main_parts.h"
#include "atom/browser/lib/bluetooth_chooser.h"
#include "atom/browser/native_window.h"
#include "atom/browser/net/atom_network_delegate.h"
#include "atom/browser/osr/osr_output_device.h"
#include "atom/browser/osr/osr_render_widget_host_view.h"
#include "atom/browser/osr/osr_web_contents_view.h"
#include "atom/browser/ui/drag_util.h"
#include "atom/browser/web_contents_permission_helper.h"
#include "atom/browser/web_contents_preferences.h"
#include "atom/browser/web_contents_zoom_controller.h"
#include "atom/browser/web_view_guest_delegate.h"
#include "atom/common/api/api_messages.h"
#include "atom/common/api/event_emitter_caller.h"
#include "atom/common/color_util.h"
#include "atom/common/mouse_util.h"
#include "atom/common/native_mate_converters/blink_converter.h"
#include "atom/common/native_mate_converters/callback.h"