Win32: Fix HDEVNOTIFY handle leak

Closes #1170.

src/win32_init.c

@@ -351,9 +351,10 @@ static HWND createHelperWindow(void)
         dbi.dbcc_devicetype = DBT_DEVTYP_DEVICEINTERFACE;
         dbi.dbcc_classguid = GUID_DEVINTERFACE_HID;
 
-        RegisterDeviceNotificationW(window,
-                                    (DEV_BROADCAST_HDR*) &dbi,
-                                    DEVICE_NOTIFY_WINDOW_HANDLE);
+        _glfw.win32.deviceNotificationHandle =
+            RegisterDeviceNotificationW(window,
+                                        (DEV_BROADCAST_HDR*) &dbi,
+                                        DEVICE_NOTIFY_WINDOW_HANDLE);
     }
 
     while (PeekMessageW(&msg, _glfw.win32.helperWindowHandle, 0, 0, PM_REMOVE))
@@ -543,6 +544,9 @@ int _glfwPlatformInit(void)
 
 void _glfwPlatformTerminate(void)
 {
+    if (_glfw.win32.deviceNotificationHandle)
+        UnregisterDeviceNotification(_glfw.win32.deviceNotificationHandle);
+
     if (_glfw.win32.helperWindowHandle)
         DestroyWindow(_glfw.win32.helperWindowHandle);
 

src/win32_platform.h

@@ -288,6 +288,7 @@ typedef struct _GLFWwindowWin32
 typedef struct _GLFWlibraryWin32
 {
     HWND                helperWindowHandle;
+    HDEVNOTIFY          deviceNotificationHandle;
     DWORD               foregroundLockTimeout;
     int                 acquiredMonitorCount;
     char*               clipboardString;