layers: LX673, CreateWin32Surface Null HWND check

Added NULL check to parameter validation, and assigned VU2505.
All we can do is check for Null. Apparently, hInstance CAN be NULL.

Change-Id: Ica5ead0514b7435ea9428dbd0018f53ff25462fd
diff --git a/layers/parameter_validation.cpp b/layers/parameter_validation.cpp
index 1991216..1cdfad1 100644
--- a/layers/parameter_validation.cpp
+++ b/layers/parameter_validation.cpp
@@ -5306,6 +5306,12 @@
 
     skip |= require_instance_extension(instance, &InstanceExtensions::khr_win32_surface, "vkCreateWin32SurfaceKHR",
                                        VK_KHR_WIN32_SURFACE_EXTENSION_NAME);
+    if (pCreateInfo->hwnd == nullptr) {
+        skip |= log_msg(my_data->report_data, VK_DEBUG_REPORT_ERROR_BIT_EXT, VK_DEBUG_REPORT_OBJECT_TYPE_UNKNOWN_EXT, 0, __LINE__,
+                        VALIDATION_ERROR_02505, LayerName,
+                        "vkCreateWin32SurfaceKHR(): hwnd must be a valid Win32 HWND but hwnd is NULL. %s",
+                        validation_error_map[VALIDATION_ERROR_02505]);
+    }
 
     skip |= parameter_validation_vkCreateWin32SurfaceKHR(my_data->report_data, pCreateInfo, pAllocator, pSurface);