Fix window class not being unregistered

The helper window kept the window class from being unregistered.

Fixes #704.

src/win32_init.c

@@ -387,6 +387,9 @@ int _glfwPlatformInit(void)
 
 void _glfwPlatformTerminate(void)
 {
+    if (_glfw.win32.helperWindow)
+        DestroyWindow(_glfw.win32.helperWindow);
+
     _glfwUnregisterWindowClassWin32();
 
     // Restore previous foreground lock timeout system setting
@@ -405,9 +408,6 @@ void _glfwPlatformTerminate(void)
     _glfwTerminateJoysticksWin32();
     _glfwTerminateThreadLocalStorageWin32();
 
-    if (_glfw.win32.helperWindow)
-        DestroyWindow(_glfw.win32.helperWindow);
-
     freeLibraries();
 }