Win32: Fix HDEVNOTIFY handle leak

Closes #1170.

src/win32_platform.h

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